DESIGN AND PROPERTIES OF NOVEL URANIUM-CONTAINING 
LAYERED AND FRAMEWORK MATERIALS 
 
 
Except where reference is made to the work of others, the work described in this 
dissertation is my own or was done in collaboration with my advisory committee.  
 This dissertation does not include proprietary or classified information. 
 
 
 
????????????????????????????????? 
Tatiana Yurievna Shvareva 
 
 
Certificate of Approval: 
 
 
 
??????????????????????????????  ?????????????????????????????? 
Peter Livant                                                             Thomas E. Albrecht-Schmitt, Chair  
Associate Professor     Associate Professor 
Chemistry      Chemistry 
 
 
 
??????????????????????????????  ?????????????????????????????? 
Holly R. Ellis      Andreas J. Illies 
Assistant Professor     Professor 
Chemistry      Chemistry 
 
 
 
        ?????????????????????????????? 
        Joe F. Pittman 
        Interim Dean 
        Graduate School 
 
DESIGN AND PROPERTIES OF NOVEL URANIUM-CONTAINING 
LAYERED AND FRAMEWORK MATERIALS 
 
 
Tatiana Yurievna Shvareva 
 
 
 
 
A Dissertation 
 
 
Submitted to 
 
 
the Graduate Faculty of 
 
 
Auburn University 
 
 
in Partial Fulfillment of the 
 
 
Requirements for the 
 
 
Degree of 
 
 
Doctor of Philosophy 
 
 
 
 
Auburn, Alabama 
December 15, 2006 
 
 iii
DESIGN AND PROPERTIES OF NOVEL URANIUM-CONTAINING 
LAYERED AND FRAMEWORK MATERIALS 
 
 
 
 
Tatiana Yurievna Shvareva 
 
 
Permission is granted to Auburn University to make copies of this dissertation at its 
discretion, upon request of individuals or institutions and at their expense. The  
author reserves all publication rights. 
 
 
 
    
 ______________________________ 
               Signature of Author 
 
 
    
 ______________________________ 
               Date of Graduation 
 iv
VITA 
 
Tatiana Yurievna (Solonskaya) Shvareva, daughter of Yuri A. Solonsky and 
Galina A. (Shabalina) Solonskaya, was born on April 8, 1973, in St. Petersburg, Russia. 
She graduated from High School N. 419, Petergoff District, St. Petersburg in 1990, and 
then from St. Petersburg State University in 1995. She obtained a Bachelor of Science 
degree in Chemistry under the direction of Dr. Nadezhda S. Grigorova and Dr. Florentina 
A. Belinskaja. She entered Graduate School at Auburn University in the fall of 2003 to 
pursue a Doctoral degree in Chemistry under the guidance of Dr. Thomas E. Albrecht-
Schmitt.  She married Alexey Y. Shvarev, son of Yevgeniy A. Shvarev and Inna N. 
(Gulika) Shvareva on July 6
th
, 1996.
 v
DISSERTATION ABSTRACT 
DESIGN AND PROPERTIES OF NOVEL URANIUM-CONTAINING 
LAYERED AND FRAMEWORK MATERIALS 
 
Tatiana Y. Shvareva 
Doctor of Philosophy, December 15, 2006 
(B. S., St. Petersburg State University, 1995) 
 
 
 
217 Typed Pages 
 
Directed by Thomas E. Albrecht-Schmitt 
 
 Ten uranyl-containing frameworks and one layered material have been 
synthesized under hydrothermal conditions. These compounds belong to eight structure 
types, not previously described. They are constructed from uranyl units in different 
coordination environments, phosphate or iodate anions, and incorporate main group or 
transition metal polyhedra. Six materials were found to have selective ion exchange 
properties. Their stabilities at elevated temperatures were examined. Thermally stable ion 
exchangers could be recommended for the further investigations under the simulated 
conditions of nuclear waste. Introduction of transition metals also leads to the appearance 
of non-linear optical and magnetic properties. A new synthetic method for the production 
of uranyl-containing framework materials is also proposed.  
 vi
ACKNOWLEDGMENT 
I wish to express my sincerest gratitude to all people, inside and outside of the 
Chemistry Department, who helped me during this work. But the very first, I would like 
to thank my research advisor, Professor Thomas E. Albrecht-Schmitt. He opened the 
world of material chemistry to me, introduced and made me feel welcome in the actinide 
research community. Now I leave his group with certain wish to spend my entire career 
in actinide material science and to make him proud.  
I would like to thank all former and present group members, whom I worked 
with: Richard, Phil, Tyler, Shehee, Jin (especially Jin), Ling, Travis, Noel and Yu for 
friendly and very helpful atmosphere in the group. In addition I need to thank little Angie 
Mustain for being very good student and very good friend.  
I am also very grateful to my committee members, Dr. Illies, Dr. Livant and Dr. 
Ellis for their advice and help along the way.  
I would like to express my especially warm ?thank you? to Dr. Lorraine Wolf and 
Dr. David Stanbury for the greatest help that I could ever imagine during my last year 
here at Auburn. They made my trip to Texas possible and I will never forget it.  
I would like to thank my parents for supporting me in any decision that I have 
ever made. I owe them a lot for never-ending patience and ?therapy? when I was 
discouraged.  
 vii
And finally I need to say that this work would never have been done without 
understanding, patience and day-by-day support of my love, Barbara, and Alexey, the 
greatest luck in my life.  
Thank you all very much. 
 viii
Style manual or journal used: 
American Chemical Society style 
________________________________________________________________________ 
 
Computer software used: 
Microsoft Word 2000, Microsoft Excel, Atom v. 6.0, Adobe Illustrator 10 
________________________________________________________________________ 
 ix
TABLE OF CONTENTS 
 
LIST OF FIGURES ...........................................................................................................xv 
LIST OF TABLES......................................................................................................... xxiii 
CHAPTER 1. INTRODUCTION ........................................................................................1 
CRYSTAL CHEMISTRY OF URANIUM (VI) UNDER 
HYDROTHERMAL CONDITIONS..............................................................2 
HIGH-LEVEL NUCLEAR WASTE (HLNW) ............................................10 
ION-EXCHANGE ........................................................................................14 
ION-EXCHANGE LAYERED AND THREE-DIMENSIONAL 
INORGANIC MATERIALS FOR SELECTIVE Cs
+
 AND Sr
2+ 
 
UPTAKE.......................................................................................................16 
MAIN GROUP AND TRANSITION METAL  
PHOSPHATES .............................................................................................24 
REFERENCES .............................................................................................27 
 
CHAPTER 2.  CRYSTAL CHEMISTRY AND ION-EXCHANGE PROPERTIES OF  
THE LAYERED POTASSIUM URANYL IODATE, K[UO
2
(IO
3
)
3
]...............................32 
ABSTRACT..................................................................................................32 
INTRODUCTION ........................................................................................33 
 x
EXPERIMENTAL........................................................................................34 
SYNTHESIS K[UO
2
(IO
3
)
3
].................................................................35 
CRYSTALLOGRAPHIC STUDIES...................................................35 
ION EXCHANGE ...............................................................................36 
RESULTS AND DISCUSSION...................................................................39 
SYNTHESIS........................................................................................39 
STRUCTURE. K[UO
2
(IO
3
)
3
]..............................................................39 
ION EXCHANGE STUDIES..............................................................42 
CONCLUSIONS...........................................................................................45 
REFERENCES .............................................................................................47 
 
CHAPTER 3.  SYNTHESES, STRUCTURES, AND ION-EXCHANGE PROPERTIES 
OF THE THREE-DIMENSIONAL FRAMEWORK URANYL GALLIUM 
PHOSPHATES, Cs
4
[(UO
2
)
2
(GaOH)
2
(PO
4
)
4
]?H
2
O AND Cs [UO
2
Ga(PO
4
)
2
] ...................50 
ABSTRACT..................................................................................................50 
INTRODUCTION ........................................................................................51 
EXPERIMENTAL........................................................................................53 
SYNTHESIS. Cs
4
[(UO
2
)
2
(GaOH)
2
(PO
4
)
4
](H
2
O) (UGaP1).................54 
SYNTHESIS. Cs[UO
2
Ga(PO
4
)
2
] (UGaP2) .........................................54 
CRYSTALLOGRAPHIC STUDIES...................................................54 
ION EXCHANGE STUDY .................................................................60 
THERMAL ANALYSIS .....................................................................60 
RESULTS AND DISCUSSION...................................................................60 
 xi
SYNTHESES.......................................................................................60 
STRUCTURE Cs
4
[(UO
2
)
2
(GaOH)
2
(PO
4
)
4
](H
2
O) (UGaP1)................61 
STRUCTURE Cs[UO
2
Ga(PO
4
)
2
] (UGaP2).........................................67 
THERMAL ANALYSIS .....................................................................70 
ION EXCHANGE ...............................................................................75 
CONCLUSIONS...........................................................................................78 
REFERENCES .............................................................................................79 
 
CHAPTER 4. SYNTHESIS, STRUCTURES AND PROPERTIES OF THE 
MULTIFUNCTIONAL URANYL VANADIUM PHOSPHATE  
FRAMEWORKS ...............................................................................................................83 
ABSTRACT..................................................................................................83 
INTRODUCTION ........................................................................................84 
EXPERIMENTAL........................................................................................85 
SYNTHESIS. Cs
2
[UO
2
(VO
2
)
2
(PO
4
)
2
]?nH
2
O (UV
V
P) .........................85 
SYNTHESIS. K
4
(UO
2
)(VO)
4
(OH)
2
(PO
4
)
4
 (KUV
IV
P).........................86 
SYNTHESIS. Rb
4
(UO
2
)(VO)
4
(OH)
2
(PO
4
)
4
 (RbUV
IV
P) .....................86 
CRYSTALLOGRAPHIC STUDIES...................................................86 
THERMAL ANALYSIS .....................................................................87 
NON-LINEAR OPTICAL PROPERTIES ..........................................87 
MAGNETIC PROPERTIES................................................................92 
ION EXCHANGE STUDIES..............................................................93 
RESULTS AND DISCUSSION...................................................................94 
 xii
SYNTHESES.......................................................................................94 
STRUCTURE. Cs
2
[UO
2
(VO
2
)
2
(PO
4
)
2
]?nH
2
O (UV
V
P)........................95 
STRUCTURE.  K
4
(UO
2
)(VO)
4
(OH)
2
(PO
4
)
4
 (KUV
IV
P) AND  
Rb
4
(UO
2
)(VO)
4
(OH)
2
(PO
4
)
4
 (RbUV
IV
P).............................................98 
THERMAL ANALYSIS ...................................................................104 
NON-LINEAR OPTICAL PROPERTIES ........................................108 
MAGNETIC PROPERTIES..............................................................108 
ION EXCHANGE STUDY ...............................................................115 
CONCLUSIONS.........................................................................................116 
REFERENCES ...........................................................................................117 
 
CHAPTER 5. HYDROTHERMAL SYNTHESIS AND STRUCTURAL 
CHARACTERIZATION OF Cs
1.52
[(UO
2
)(TiOH
0.48
)(PO
4
)
2
]?nH
2
O AND 
Cs
1.35
[(UO
2
)(GeOH
0.65
)(PO
4
)
2
]?nH
2
O..............................................................................120 
ABSTRACT................................................................................................120 
INTRODUCTION ......................................................................................121 
EXPERIMENTAL......................................................................................123 
SYNTHESIS. Cs
1.52
[(UO
2
)(TiOH
0.48
)(PO
4
)
2
]?nH
2
O (UTiP) .............124 
SYNTHESIS. Cs
1.35
[(UO
2
)(GeOH
0.65
)(PO
4
)
2
]?nH
2
O (UGeP)...........124 
CRYSTALLOGRAPHIC STUDIES.................................................125 
RESULTS AND DISCUSSION.................................................................129 
SYNTHESES.....................................................................................129 
STRUCTURE ....................................................................................129 
 xiii
CONCLUSIONS.........................................................................................137 
REFERENCES ...........................................................................................140 
 
CHAPTER 6. GENERAL ROUTE TO THREE-DIMENSIONAL FRAMEWORK 
URANYL TRANSITION METAL PHOSPHATES WITH ATYPICAL  
STRUCTURAL MOTIFS: THE CASE EXAMPLES OF 
Cs
2
{(UO
2
)
4
[Co(H
2
O)
2
]
2
(HPO
4
)(PO
4
)
4
}, Cs
2
{(UO
2
)
4
[Ni(H
2
O)
2
]
2
(HPO
4
)(PO
4
)
4
}, 
AND Cs
3+x
[(UO
2
)
3
CuH
4-x
(PO
4
)
5
]?H
2
O............................................................................144
 
ABSTRACT................................................................................................144 
INTRODUCTION ......................................................................................145 
EXPERIMENTAL......................................................................................146 
SYNTHESIS. Cs
2
{(UO
2
)
4
[Co(H
2
O)
2
]
2
(HPO
4
)(PO
4
)
4
}(UCoP).........146 
SYNTHESIS. Cs
2
{(UO
2
)
4
[Ni(H
2
O)
2
]
2
(HPO
4
)(PO
4
)
4
} (UNiP) .........147 
SYNTHESIS. Cs
3+x
[(UO
2
)
3
CuH
4-x
(PO
4
)
5
]?H
2
O (UCuP)...................147 
X-RAY STRUCTURAL ANALYSIS...............................................147 
THERMAL ANALYSIS ...................................................................148 
UV-VIS-NIR DIFFUSE REFLECTANCE SPECTRA.....................156 
MAGNETIC PROPERTIES..............................................................156 
ION EXCHANGE STUDIES............................................................157 
RESULTS AND DISCUSSION 158 
SYNTHESES.....................................................................................158 
STRUCTURE.  Cs
2
{(UO
2
)
4
[Co(H
2
O)
2
]
2
(HPO
4
)(PO
4
)
4
}(UCoP) 
AND Cs
2
{(UO
2
)
4
[Ni(H
2
O)
2
]
2
(HPO
4
)(PO
4
)
4
} (UNiP) .......................159 
 xiv
STRUCTURE . Cs
3+x
[(UO
2
)
3
CuH
4-x
(PO
4
)
5
]?H
2
O (UCuP)................162 
UV-VIS-NIR DIFFUSE REFLECTANCE STUDY.........................171 
MAGNETIZATION MEASUREMENTS.........................................174 
THERMAL ANALYSIS ...................................................................178 
ION EXCHANGE PROPERTIES.....................................................183 
CONCLUSIONS ........................................................................................184 
REFERENCES ...........................................................................................186 
CHAPTER 7. SUMMARY..............................................................................................189 
 
 xv
LIST OF FIGURES 
 
Figure 1. 1.  The UO
2
2+ 
cation in tetragonal bipyramidal, pentagonal bipyramidal, and 
hexagonal bipyramidal environments as common building units for uranyl 
structure formation. They can be interconnected by corner- or edge- 
sharing with each other or other building units in order to construct  
different structure types ..................................................................................5 
Figure 1. 2.  The structure of (C
4
N
2
H
12
)U
2
O
4
F
6 
composed of only uranyl pentagonal 
bipyramids (green). Piperazinium cations are located in the channels of  
the framework .................................................................................................6 
Figure 1. 3.  The structure of K
2
[(UO
2
)
2
(VO)
2
(IO
6
)
2
O]?H
2
O is built from distorted  
octahedral building units only.  UO
6
 polyhedra are shown in green,  
VO
6
 ?in light blue, and IO
6
 ? in red color. K
+
 cations along with water 
molecules occupy the tunnels. The UO
2
2+
 uranyl unit exists as a nearly 
linear trans dioxo unit .....................................................................................7 
Figure 1. 4.  The structure of Li
2
(UO
2
)
4
(WO
4
)O is an example of a three-dimensional  
structure with no channels. Li
+
 cations located in the voids of uranyl  
tungstate layers are not seen from this projection. UO
6
 polyhedra are  
green, WO
6
 ? shown in violet color................................................................9 
 xvi
Figure 1. 5.  Chiral channels extended along c axis make the uranyl molybdate  
(NH
4
)
4
[(UO
2
)
5
(MoO
4
)
7
](H
2
O)
5
 potentially applicable for enantio- 
selective separation. NH
4
+
 cations are not shown, UO
7
 polyhedra  
are green, MoO
4
 tetrahedra are blue .............................................................11 
Figure 1. 6.  A view of the crystal structure of Na
2
Ti
2
O
3
(SiO
4
)?H
2
O along the [001]  
direction. Yellow squares depict TiO
6
 octahedra, orange - SiO
4
  
tetrahedra, green balls ? Na
+
 cations. Four out of the total eight Na
+
  
cations are located in the channels, the other four (on the silicate  
groups) ? in small cavities. Copied from reference 50 with author?s 
permission.....................................................................................................18 
Figure 1. 7.  This fragment depicts interconnection of octahedral units in the structure  
of Na
2
Nb
2-x 
Ti
x
O
6-x
(OH)
x
?H
2
O. Blue polyhedra represent disordered  
NbO
6
 and TiO
6
 octahedra. Yellow polyhedra are Na coordination spheres,  
participating in the framework. Copied from reference 52 with author?s 
permission.....................................................................................................23 
Figure 2. 1.  A view of the pentagonal bipyramidal coordination environment  
around uranium center in KUI that is formed from UO
2
2+
 linear  
cation connected with five iodate groups through the  
equatorial plane.............................................................................................41 
Figure 2. 2.  An illustration of the 
2
?
[UO
2
(IO
3
)
3
]
1?
 sheets in KUI that extend in the 
[ab] plane ......................................................................................................43 
Figure 2. 3.  A view along the b axis of KUI showing that the monodentate iodate  
anion protrudes in between the layers, providing its terminal oxo  
 xvii
atoms for forming interactions with the K
+
 cations that reside between  
the layers .......................................................................................................44 
Figure 3. 1.  A view of the one-dimensional 
1
?
[Ga(OH)(PO
4
)
2
]
4?
 chains composed  
of corner-sharing GaO
6
 octahedra and bridging PO
4
 tetrahedra that  
extend along the c axis in Cs
4
[(UO
2
)
2
(GaOH)
2
(PO
4
)
4
]?H
2
O (UGaP1).   
50% probability ellipsoids are depicted........................................................63 
Figure 3. 2.  A depiction of the one-dimensional 
1
?
[UO
2
(PO
4
)
2
]
4?
 chains in 
Cs
4
[(UO
2
)
2
(GaOH)
2
(PO
4
)
4
]?H
2
O (UGaP1).  50% probability ellipsoids  
are depicted ...................................................................................................67 
Figure 3. 3.  An illustration of the three-dimensional 
3
?
[(UO
2
)
2
(GaOH)
2
(PO
4
)
4
]
4?
  
anionic lattice of Cs
4
[(UO
2
)
2
(GaOH)
2
(PO
4
)
4
]?H
2
O (UGaP1) that has  
intersecting channels running down the b and c axes.  These channels  
house Cs
+
 cations and water molecules.  Cs is shown in magenta,  
UO
7
 pentagonal bipyramids are shown in green, GaO
6
 octahedra in  
blue, and PO
4
 tetrahedra in yellow ...............................................................69 
Figure 3. 4.  A view of the one-dimensional 
1
?
[Ga(PO
4
)
2
]
3? 
gallium phosphate  
chains in Cs[UO
2
Ga(PO
4
)
2
] (UGaP2) formed from fused eight- 
membered rings of alternating corner-shared GaO
4
 and PO
4
 tetrahedra.  
50% probability ellipsoids are depicted........................................................70 
Figure 3. 5.  An illustration of the one-dimensional 
1
?
[UO
2
(PO
4
)
2
]
4?
 chains in  
Cs[UO
2
Ga(PO
4
)
2
] (UGaP2).  50% probability ellipsoids are depicted ........72 
 xviii
Figure 3. 6.  A depiction of the three-dimensional 
3
?
[UO
2
Ga(PO
4
)
2
]
1? 
framework in 
Cs[UO
2
Ga(PO
4
)
2
] (UGaP2) with intersecting channels running down  
the a and b axes.  Cs is shown in magenta, UO
7
 pentagonal bipyramids  
are shown in green, GaO
4
 tetrahedra in blue, and PO
4
 tetrahedra in  
yellow............................................................................................................73 
Figure 3. 7.  DSC data of UGaP1 demonstrate relative stability of the structure at  
temperatures below 400 ?C. Two peaks at 150 ?C and 172 ?C  
correspond to lost of surface and interstitial water respectively...................74 
Figure 3. 8.  DSC data of UGaP2.......................................................................................77 
Figure 4. 1.  Depiction of the channels of UV
V
P, extended along b and c axes,  
occupied by Cs
+
 cations. Green ? uranium, blue ? vanadium,  
yellow ? phosphorus, purple ? cesium centers .............................................97 
Figure 4. 2.  The fundamental building unit of UV
V
P shown in 50% probability  
thermal ellipsoids........................................................................................100 
Figure 4. 3.  Thermal ellipsoid plot of the fundamental unit of  
K
4
(UO
2
)(VO)
4
(OH)
2
(PO
4
)
4 
(KUV
IV
P) and Rb
4
(UO
2
)(VO)
4
(OH)
2
(PO
4
)
4 
 
(RbUV
IV
P) at 50% probability....................................................................101 
Figure 4. 4.  Depiction of essential building blocks of the structures of KUV
IV
P and 
RbUV
IV
P.  V
2
O
9
 dimer, constructed from two vanadium octahedra,  
sharing two equatorial and one axial oxygen atoms (top) and vanadyl  
phosphate layers (bottom). Cations (purple) occupy the channels  
2.8 ? ? 4.4 ? along c axis. Blue - vanadium polyhedra, yellow ?  
phosphate groups ........................................................................................104 
 xix
Figure 4. 5.  Depiction of the channels in the framework of KUV
IV
P and  
RbUV
IV
P, filled with K
+
 or Rb
+ 
cations, extended along a axis.  
Blue - vanadium, yellow ? phosphorus, green ? uranium centers,  
purple ? K
+
 or Rb
+
 cations ..........................................................................106 
Figure 4. 6.  A view of the framework of KUV
IV
P and RbUV
IV
P along the b axis ........107 
Figure 4. 7.  DSC data for the structure of UV
V
P demonstrate thermal stability  
up to 510 ?C ................................................................................................108 
Figure 4. 8.  DSC data for the structure of KUV
IV
P. Several endothermic events  
between 160 ?C and 550 ?C reveal gradual structural transformations  
with increase of temperature.......................................................................110 
Figure 4. 9.  Magnetization of UV
V
P as a function of applied magnetic field at 5 K. 
Line is the linear fit to the data ...................................................................111 
Figure 4. 10.  Magnetic susceptibility of UV
V
P as a function of temperature  
with a 10000 G magnetic field ...................................................................112 
Figure 4. 11.  Magnetization of RbUV
IV
P as a function of applied magnetic field  
at 5 K.  Line is the linear fit to the data ......................................................114 
Figure 4. 12.  Magnetic susceptibility of RbUV
IV
P as a function of temperature.   
Line is the fit to Curie-Weiss behavior.  Inset show the temperature  
dependence of the inverse magnetic susceptibility.....................................115 
Figure 5. 1.  Thermal ellipsoid plot of Cs
1.52
[(UO
2
)(TiOH
0.48
)(PO
4
)
2
]?nH
2
O (UTiP)  
shown at 50% probability ...........................................................................132 
Figure 5. 2.  Depiction of one-dimensional titanium phosphate or germanium  
phosphate and uranyl phosphate chains in UTiP or UGeP.  
 xx
Violet - titanium or germanium polyhedra, yellow-phosphate  
tetrahedra, green-uranyl building units.......................................................133 
Figure 5. 3.  The framework of UTiP and UGeP. The channels along the c axis  
are filled with Cs
+
 cations (purple) and water molecules (red). Violet  
octahedra represent Ti or Ge, yellow ? phosphate, and green ? uranium 
centers .........................................................................................................137 
Figure 6. 1.  The fundamental building unit of UCoP includes three  
crystallographically unique U centers, two in pentagonal bipyramidal,  
and one in hexagonal bipyramidal environment, three tetrahedral P  
centers, and Co octahedra. 50% probability thermal ellipsoids are  
represented. UNiP is isostructural with UCoP............................................162 
Figure 6. 2.  View down the c axis of the uranyl phosphate layers in UCoP and  
UNiP. One of the phosphate anions is disordered and is shown in  
ball-and-stick format. Uranium polyhedra are in green and  
phosphate are in yellow ..............................................................................163 
Figure 6. 3. An illustration of the three-dimensional structure of UCoP and  
UNiP as viewed down the b axis. Uranium polyhedra are in green, 
phosphate in yellow, cobalt or nickel in orange. Purple centers  
represent the Cs
+
 cations.............................................................................165 
Figure 6. 4.  A view of the uranyl tetragonal and pentagonal bipyramids, square  
planar Cu and phosphate tetrahedra in UCuP with 50% probability  
ellipsoids .....................................................................................................169 
Figure 6. 5.  Depiction of uranyl phosphate layers in UCuP. Uranyl polyhedra are  
 xxi
in green and phosphates are in yellow ........................................................171 
Figure 6. 6.  View of the three-dimensional structure of UCuP wherein the Cu
II
  
centers link uranyl phosphate layers together. Uranium polyhedra are  
in green, phosphate in yellow, and copper in blue. Some of the Cs
+
  
sites have been omitted for clarity ..............................................................172 
Figure 6. 7.  UV-vis-NIR diffuse reflectance spectrum of UCoP. F(R) corresponds  
to Kubelka-Monk function and relates reflectance data to the  
absorption spectra.
37 ..............................................................................................................................
174 
Figure 6. 8.  UV-vis-NIR diffuse reflectance spectrum of UNiP. F(R) corresponds  
to Kubelka-Monk function and relates reflectance data to the  
absorption spectra.
37
....................................................................................175 
Figure 6. 9.  UV-vis-NIR diffuse reflectance spectrum for UCuP. F(R) corresponds  
to Kubelka-Monk function and relates reflectance data to the  
absorption spectra.
37
....................................................................................177 
Figure 6. 10.  Magnetization of UCoP as a function of applied magnetic field  
at 5 K.  Line is the linear fit to the data.......................................................178 
Figure 6. 11.  Magnetic susceptibility of UCoP as a function of temperature.   
Line is the fit to Curie-Weiss behavior.  Inset show the temperature  
dependence of the inverse magnetic susceptibility with a linear fit. ..........179 
Figure 6. 12.  Magnetization of UCuP as a function of applied magnetic field at 5 K.   
Line is the linear fit to the data. ..................................................................180 
Figure 6. 13.  Magnetic susceptibility of UCuP as a function of temperature.   
Line is the fit to Curie-Weiss behavior.  Inset show the temperature  
 xxii
dependence of the inverse magnetic susceptibility.....................................181 
Figure 6. 14.  DSC data for UCoP ...................................................................................183 
Figure 6. 15.  DSC data for UCuP ...................................................................................184 
 xxiii
LIST OF TABLES 
Table 1. 1.  The Most Significant Contributors to the Radiation Dose from HLNW........13 
Table 1. 2.  Crystallographic Data for Na
2
Ti
2
O
3
(SiO
4
)?H
2
O (TiSi-1),  
HM
3
Ti
4
O
4
(SiO
4
)?H
2
O (TiSi-2) and Na
2
Nb
2-x
M
x
O
6-x
(OH)
x
?H
2
O  
(SOMS).........................................................................................................19 
Table 1. 3.  The Comparative Table of Distribution Coefficients for Sr
2+
, K
DSr
,  
of Na
4
Ti
9
O
20
?nH
2
O, Na
2
Ti
2
O
3
(SiO
4
)?H
2
O, and HK
3
Ti
4
O
4
(SiO
4
)?H
2
O
64
  
in Different HLNW Simulants......................................................................21 
Table 2. 1.  Crystallographic Data for K[UO
2
(IO
3
)
3
] (KUI)..............................................37 
Table 2. 2.  Atomic Coordinates and Equivalent Isotropic Displacement Parameters  
for K[UO
2
(IO
3
)
3
] (KUI)................................................................................38 
Table 2. 3.  Selected Bond Distances (?) and Angles (?) for K[UO
2
(IO
3
)
3
] (KUI) ..........40 
Table 3. 1.  Crystallographic Data for Cs
4
[(UO
2
)
2
(GaOH)
2
(PO
4
)
4
]?H
2
O (UGaP1)  
and Cs[UO
2
Ga(PO
4
)
2
] (UGaP2) ...................................................................57 
Table 3. 2.  Atomic Coordinates and Equivalent Isotropic Displacement Parameters  
for Cs
4
[(UO
2
)
2
(GaOH)
2
(PO
4
)
4
]?H
2
O (UGaP1) .............................................58 
Table 3. 3.  Atomic Coordinates and Equivalent Isotropic Displacement Parameters  
for Cs[UO
2
Ga(PO
4
)
2
] (UGaP2) ....................................................................60 
Table 3. 4.  Selected Bond Distances (?) and Angles (
o
) for Cs
4
[(UO
2
)
2
(GaOH)
2
(PO
4
)
4
]
(UGaP1) ........................................................................................................64 
 xxiv
Table 3. 5.  Selected Bond Distances (?) and Angles (
o
) for Cs[UO
2
Ga(PO
4
)
2
]  
(UGaP2) ........................................................................................................72 
Table 4. 1.  Crystallographic Data for Cs
2
[UO
2
(VO
2
)
2
(PO
4
)
2
]?nH
2
O (UV
V
P),  
K
4
(UO
2
)(VO)
4
(OH)
2
(PO
4
)
4
 (KUV
IV
P) and  
Rb
4
(UO
2
)(VO)
4
(OH)
2
(PO
4
)
4
 (RbUV
IV
P)......................................................89 
Table 4. 2.  Atomic Coordinates and Equivalent Isotropic Displacement Parameters  
for Cs
2
[UO
2
(VO
2
)
2
(PO
4
)
2
]?nH
2
O (UV
V
P) ....................................................90 
Table 4. 3.  Atomic Coordinates and Equivalent Isotropic Displacement  
Parameters for K
4
(UO
2
)(VO)
4
(OH)
2
(PO
4
)
4
 (KUV
IV
P).................................91 
Table 4. 4.  Atomic Coordinates and Equivalent Isotropic Displacement Parameters 
for Rb
4
(UO
2
)(VO)
4
(OH)
2
(PO
4
)
4
 (RbUV
IV
P)................................................92 
Table 4. 5.  Selected Bond Distances (?) and Angles (?) for  
Cs
2
[UO
2
(VO
2
)
2
(PO
4
)
2
]?nH
2
O (UV
V
P)..........................................................98 
Table 4. 6.  Selected Bond Distances (?) and Angles (?) for  
K
4
(UO
2
)(VO)
4
(OH)
2
(PO
4
)
4 
(KUV
IV
P). Data for   
Rb
4
(UO
2
)(VO)
4
(OH)
2
(PO
4
)
4
 (RbUV
IV
P) are given in parathensis.............102 
Table 5. 1.  Crystallographic Data for Cs
1.52
[(UO
2
)(TiOH
0.48
)(PO
4
)
2
]?nH
2
O  
(UTiP) and Cs
1.35
[(UO
2
)(GeOH
0.65
)(PO
4
)
2
]?nH
2
O (UGeP) ........................127 
Table 5. 2.  Atomic Coordinates and Equivalent Isotropic Displacement Parameters  
for Cs
1.52
[(UO
2
)(TiOH
0.48
)(PO
4
)
2
]?nH
2
O (UTiP)........................................128 
Table 5. 3.  Atomic Coordinates and Equivalent Isotropic Displacement Parameters  
for Cs
1.35
[(UO
2
)(GeOH
0.65
)(PO
4
)
2
]?nH
2
O (UGeP)......................................129 
Table 5. 4.  Selected Bond Distances (?) and Angles (?) for  
 xxv
Cs
1.52
[(UO
2
)(TiOH
0.48
)(PO
4
)
2
]?nH
2
O (UTiP)..............................................135 
Table 5. 5.  Selected Bond Distances (?) and Angles (?) for  
Cs
1.35
[(UO
2
)(GeOH
0.65
)(PO
4
)
2
]?nH
2
O (UGeP) ...........................................136 
Table 6. 1.  Crystallographic Data for Cs
2
{(UO
2
)
4
[Co(H
2
O)
2
]
2
(HPO
4
)(PO
4
)
4
}  
(UCoP),  Cs
2
{(UO
2
)
4
[Ni(H
2
O)
2
]
2
(HPO
4
)(PO
4
)
4
} (UNiP) and  
Cs
3+x
[(UO
2
)
3
CuH
4-x
(PO
4
)
5
]?H
2
O (UCuP) ...................................................151 
Table 6. 2.  Atomic Coordinates and Equivalent Isotropic Displacement Parameters  
for Cs
2
{(UO
2
)
4
[Co(H
2
O)
2
]
2
(HPO
4
)(PO
4
)
4
} (UCoP)...................................152 
Table 6. 3.  Atomic Coordinates and Equivalent Isotropic Displacement Parameters  
for Cs
2
{(UO
2
)
4
[Ni(H
2
O)
2
]
2
(HPO
4
)(PO
4
)
4
} (UNiP)....................................154 
Table 6. 4.  Atomic Coordinates and Equivalent Isotropic Displacement Parameters  
for Cs
3+x
[(UO
2
)
3
CuH
4-x
(PO
4
)
5
]?H
2
O (UCuP)..............................................156 
Table 6. 5.  Selected Bond Distances (?) and Angles (?) for 
Cs
2
{(UO
2
)
4
[Co(H
2
O)
2
]
2
(HPO
4
)(PO
4
)
4
} (UCoP) ........................................166 
Table 6. 6.  Selected Bond Distances (?) and Angles (?) for  
Cs
2
{(UO
2
)
4
[Ni(H
2
O)
2
]
2
(HPO
4
)(PO
4
)
4
} (UNiP)..........................................167 
Table 6. 7.  Selected Bond Distances (?) and Angles (?) for  
Cs
3+x
[(UO
2
)
3
CuH
4-x
(PO
4
)
5
]?H
2
O (UCuP) ...................................................170 
 1 
CHAPTER 1 
INTRODUCTION 
 The successful test of the first nuclear reactor at the University of Chicago in 
19421 changed the course of history.  This experiment initiated not only the ?Manhattan 
Project?, and later the production of nuclear power,2  but it also produced the first portion 
of highly radioactive nuclear waste.  Since that time the search for appropriate long-term 
storage conditions for high-level nuclear waste (HLNW) and spent nuclear fuel (SNF), as 
well as investigations into possibilities for the reduction of the total nuclear waste 
amounts became an issue of world-wide importance.3-6 The detailed knowledge about the 
fundamental chemistry of actinides is an essential basis for predicting the behavior of 
waste under different environmental conditions.  Interactions of SNF with underground 
water and formation of the alteration phases under storage conditions6-9, or the mobility 
of actinides in soils6 are just a couple of selected issues that will be addressed herein.  
 The separation of the major fission products 137Cs and 90Sr from SNF is critical to 
the proper storage of radioactive waste.3,4 These two radionuclides with half-lives of 30.2 
and 28.5 years, respectively, are the source of 99% of the present radioactivity in the 
HLNW storage tanks.  They are distributed between salt cake ? the solid portion of the 
waste on the top, and liquid portions - hydroxide sludge and alkaline supernatant.3 The 
removal of Cs+ and Sr2+ will significantly reduce the total amount of nuclear waste.  One 
of the proposed techniques for such removal, ion-exchange, also will allow the transfer of 
 2 
Cs+ and Sr2+ from liquid to the solid phase, and will make the final disposal possible.  
This method requires the use of layered or framework materials, that should have a high 
capacity and selectivity for Cs+ and Sr2+, be resistant to elevated temperature and 
radiation damage, and should be easily synthesized.10  
The general purpose of this research project is to expand the existing knowledge 
of the crystal chemistry of uranium compounds with novel structural topologies, to 
develop new synthetic methods, and address potential applications of these materials.  
The other major goal is to synthesize uranium-containing layered or three-dimensional 
compounds with ion-exchange properties selective for Cs+ or Sr2+.  These materials in 
exchanged form will be able to tightly hold 137Cs or 90Sr, and provide safe and dense 
storage environments for U and 137Cs or 90Sr simultaneously.  
 
CRYSTAL CHEMISTRY OF URANIUM (VI) UNDER HYDROTHERMAL 
CONDITIONS  
 Uranium is found as a component of approximately 200 mineral crystal 
structures.11,12  The majority of these minerals are present in the oxidizing zones of U 
deposits and should be accurately studied in both prospects as deeply stored nuclear 
waste and as potential products of oxidation of SNF and its interaction with water 
(alteration phases) in the geological repository locations.  Precise investigation of the 
structures, as well as the stability and properties of uranium compounds synthesized 
under hydrothermal conditions, will help researchers to understand and predict the 
behavior of uranium phases in expected geological sites.  
 
 3 
 The term ?hydrothermal synthesis? usually refers to all reactions having water as 
a solvent carried out at temperatures between the boiling and supercritical points of water 
and at pressures above 1 bar.13   These temperature and pressure conditions were chosen 
for our experiments due to similar conditions for the geological formation of minerals.  In 
addition, hydrothermal synthesis potentially allows for the synthesis of compounds with 
lower densities through the incorporation of water in the structures versus more dense 
products that are typically isolated from high temperature reactions.  
 In the majority of both uranium-containing solids and solutions that are of an 
oxidizing nature, U is present in the +6 oxidation state.  In order to maintain such a high 
positive charge, two short U=O bonds in trans arrangement with an average U=O 
distance of 1.79(3) ? are formed,12 yielding approximately linear [UO2]2+ cation.  
Because these two oxygen atoms donate their electron density to the uranium center and 
hence stabilize the high oxidation state of U, they seldom participate in bond formation 
with other units.  According to bond valence sum calculations based on the uranyl-
oxygen distances, these two axial oxygen atoms contribute more than half to the valence 
of the uranium center.14  The concept of bond valence sum can be used in solid state 
chemistry in order to estimate bond lengths of a metal in a given oxidation state or to 
calculate the valence of the atom from the known distances.15  
 Interactions between uranyl and other donor atoms occur in the equatorial plane 
where the metal center can be coordinated with four, five, or six ligands, with distances 
ranging from 2.2 ? to 2.6 ?.  Thus, traditionally the basic building unit for uranyl-
containing compounds can be drawn as tetragonal, pentagonal, or hexagonal bipyramids 
terminated at each apex by two uranyl oxygen atoms.  These three basic uranyl polyhedra 
 4 
can be combined through various modes of corner or edge sharing with each other 
(Figure 1.1), or by bridging with other building units, to yield a myriad of crystal 
structure topologies.11,12  
 Due to the presence of two terminal oxygen atoms, one direction for the 
connectivity in uranyl bipyramids is eliminated, yielding structures that are generally 
layered.  In fact, more than 65% of all known structures of uranyl containing compounds 
are sheets.11,12 For the formation of the compounds with three-dimensional structure, 
where building blocks are interconnected in all three directions, usually, but not always, 
non-uranyl polyhedra are incorporated into the structure that give additional directions 
for bond formation.  
 There are several strategies for the building of three-dimensional structures that 
contain uranium.  Very few three-dimensional structures are built from uranyl building 
units only.16-18 For instance, (C4N2H12)U2O4F6 consists of only one type of building units 
- UO2F5 pentagonal bipyramids, which are connected by U-F-U bonds.18  This structure 
also can be described as an open-framework because of the presence of several large 
channels, extended along different directions that are filled with charge-balancing 
piperazinium cations (Figure 1.2).  
 The other synthetic approach includes incorporation of octahedra of other metals 
such as V or W in the structure.19,20  K2[(UO2)2(VO)2(IO6)2O]?H2O (Figure 1.3) is 
constructed entirely from distorted octahedral building units.19 The UO6 distortion in this 
structure is associated with the formation of short uranyl bonds and nonequality of 
equatorial U-O bond lengths, VO6 ? with the presence of short vanadyl V=O bond
 5 
 
 
  
 
 
Figure 1. 1.  The UO22+ cation in tetragonal bipyramidal, pentagonal bipyramidal, and 
hexagonal bipyramidal environments as common building units for uranyl structure 
formation.  They can be interconnected by corner- or edge-sharing with each other or 
other building units in order to construct different structure types.  
 6 
 
 
 
 
 
 
 
 
 
 
 
Figure 1. 2.  The structure of (C4N2H12)U2O4F6 composed of only uranyl pentagonal 
bipyramids (green). Piperazinium cations are located in the channels of the framework.  
 7 
 
 
 
 
 
 
Figure 1. 3.  The structure of K2[(UO2)2(VO)2(IO6)2O]?H2O is built from distorted 
octahedral building units only.  UO6 polyhedra are shown in green, VO6 ? in light blue, 
IO6 ? in red, and K+ cation ? in magenta . K+ cations along with water molecules occupy 
the tunnels.   
 8 
(1.58(1) ?) and a long bond in the trans-position relative to V=O (2.38(1) ?). IO6 
octahedra also show variations in I-O bond length from 1.84(1) ? to 1.93(1) ?.  The 
octahedra create an open-framework structure with channels in two perpendicular 
directions, both occupied by K+ cations.  
 Li2(UO2)4(WO4)O (Figure 1.4) is an example of a three-dimensional, but non-
open-framework structure.20 Very small channels are present only in the [110] direction, 
and they are not filled with cations. Instead, Li+ cations are located within the voids in the 
plane of layers.  Despite the absence of channels, this material was reported to have high 
cationic conductivity, comparable with Li 
-alumina and LiSiCON materials.20 
 Most of the uranyl-containing three-dimensional materials are built from uranyl 
units and tetrahedral anions, such as phosphate or arsenate,21-26 sulfate,27 silicate,28-33 
vanadate 34,35  or others.  These structures can be constructed in many different manners, 
such as the interconnection of one-dimensional chains or layers by single building blocks, 
intersection of several one-dimensional chains extended along different axes, or by other 
methods.  
 We hypothesized that the introduction of octahedral building units containing 
main group (Ga, In, Ge) or transitional metal (Ti, V, Co Ni, Cu) to uranyl and tetrahedral 
building blocks might lead to the formation of new types of three-dimensional structures 
with new topologies.  
 There are 54 framework types known for uranyl-containing compounds today.12 
Due to the vast amount of stored depleted uranium with low radioactivity that has to be 
utilized in the near-term perspective, an extensive search for new practical applications 
  
 9 
  
 
 
 
 
 
 
 
Figure 1. 4.  The structure of Li2(UO2)4(WO4)O is an example of a three-dimensional 
structure with no channels.  Li+ cations located in the voids of uranyl tungstate layers are 
not seen from this projection.  UO6 polyhedra are green, WO6 ? shown in violet color. 
 10 
for these structures is being conducted. For example, Na(UO2)4(VO4)3 and 
Li(UO2)4(VO4)3 can serve as ionic conductors due to the migration of Na+ and Li+ cations 
in two intersecting channels within the structure.34  
 Chiral uranyl molybdates [(C2H5)2NH2]2(UO2)4(MoO4)5(H2O)](H2O)36 and 
(NH4)4[(UO2)5(MoO4)7](H2O)537 (Figure 1.5) both have large channels extended along 
the [001] direction with a chiral topology as required by space group (P6522 and P61 
respectively).  In terms of tubular building units, the internal structure of these channels 
can be described as a double-helix, where both chains form spirals with axes parallel to 
[001].  Structures with these types of channels can potentially find applications in 
enantioselective separation and catalysis.37 
 We proposed that our new uranyl main group or transition metal phosphate 
materials synthesized within this project can potentially serve as ion-exchange and 
storage materials for immobilization of radioactive 137Cs and 90Sr from nuclear waste 
solutions. 
 
HIGH-LEVEL NUCLEAR WASTE (HLNW) 
 At the present time, HLNW produced in the processing of uranium and 
plutonium, is stored in 273 underground carbon-steel tanks.3 This storage strategy needs 
to be changed due to leakage of radioactive waste into the soil, and the potential long-
term impact of this to the environment.  The deep geological repository in the Yucca 
Mountain area, Nevada, was proposed as the safest way for ultimate disposal.  
 
 
 11 
 
 
 
 
 
Figure 1. 5.  Chiral channels extended along the c axis make the uranyl molybdate 
(NH4)4[(UO2)5(MoO4)7](H2O)5 potentially applicable for enantio-selective separation. 
NH4+ cations are not shown, UO7 polyhedra are green, MoO4 tetrahedra are blue.  
 12 
 It is apparent that the application of geological disposal methods requires 
pretreatment of highly inhomogeneous waste in order to convert it to a solid form and to 
separate long-living isotopes pertinent for geological deposition from short-living 
isotopes and low-activity portions.  
 The main input to the present radioactivity in the tanks is from 137Cs and 90Sr.  
These isotopes are major dose contributors only during the first 100 years of deposition.  
(Table 1.1) Their removal from the tanks will significantly reduce the total amount of 
waste prepared for the geological repository and will make this process more reasonable.  
 Solvent extraction is the method currently used for 137Cs and 90Sr separation.3 90Sr 
is extracted by 4,4?(5?)-di-(tert-butylcyclohexano)-18-crown-6 in an organic solution of 
1.5 M TBP and hydrocarbon diluent called Isopar L (SREX process).3,4 Tests  in actual 
waste containers demonstrated that SREX reduces the activity of waste in the tanks after 
90Sr extraction to 0.04 Ci/L, which can be considered as low-level waste activity.3 137Cs 
can be separated by various crown ethers or cobalt dicarbollide dissolved in a very polar 
solvent such as nitrobenzene.3,4 This process removes over 99.998% of the 137Cs. In order 
to co-extract both radionuclides simultaneously, polyethylene glycol can be added to the 
polar solvent-cobalt dicarbollide system.3  
 Other techniques such as in-tank precipitation of 137Cs with sodium 
tetraphenylborate or membrane separation were proposed for removal of 137Cs and 90Sr, 
but several issues, such as pretreatment of the solutions, capacity of the separation, 
stability of precipitating agents and membranes in actual waste, and volume dependence 
still need to be optimized.3 
   
 13 
Table 1. 1.  The most significant contributors to the radiation dose from HLNW.6 
Activity (Ci/canister), Time out of Reactor Radionuclide Half-life 
10 years 100 years 1000 years 10000 years 
90Sr 29 years 1.4?105 1.5?104 3.5?10-6 0 
90Y 64 years 1.4?105 1.5?104 3.5?10-6 0 
99Tc 2.13?105 years 3.2?101 3.2?101 3.2?101 3.2?101 
106Ru 369 days 1.3?103 0 0 0 
106Rh 2.18 hours 1.3?103 0 0 0 
125Sb 2.73 years 1.6?103 0 0 0 
129I 1.59?105 years 1.8?10-4 1.8?10-4 1.8?10-4 1.8?10-4 
134Cs 2.06 years 1.9?104 0 0 0 
137Cs 30.1 years 2.0?105 2.4?104 2.3?10-5 0 
144Ce 284.4 days 3.5?102 0 0 0 
147Pm 2.64 years 1.8?104 8.1?10-7 0 0 
154Eu 8.6 years 1.0?104 2.1?102 0 0 
226Ra 1600 years 2.5?10-7 2.6?10-6 1.6?10-4 6.5?10-3 
229Th 7340 years 9.6?10-8 1.7?10-6 1.6?10-4 1.3?10-2 
230Th 7.7?104 years 4.9?10-5 7.4?10-5 8.8?10-4 8.1?10-3 
213Pa 3.25?104 years 5.7?10-5 5.7?10-5 6.0?10-5 8.8?10-5 
233U 1.58?105 years 3.4?10-5 3.4?10-5 3.5?10-3 3.6?10-2 
237Np 2.14?106 years 8.1?10-1 8.1?10-1 8.8?10-1 8.8?10-1 
238Pu 87.8 years 2.4?102 1.2?102 2.8?10-1 0 
239Pu 2.439?104 years 3.8 3.8 4.7 9.6 
240Pu 6540 years 1.0?101 2.0?101 1.8?101 7.3 
241Pu 15 years 7.4?101 1.1?101 7.2?10-1 3.4?10-1 
241Am 433 years 4.1?102 3.8?102 8.1?101 3.4?10-1 
243Am 7370 years 4.0?101 4.0?101 3.7?101 1.7?101 
242Cm 163 days 1.6?101 1.1?101 1.8?10-1 0 
244Cm 17.9 years 4.0?103 1.3?102 0 0 
 
 
 
 
 
 
 14 
Ion-exchange is also considered as a prospective method for the separation of short-lived 
137Cs and 90Sr radionuclides.  
 
ION-EXCHANGE 
 Ion-exchange is a stoichiometric equilibrium process between the ions of the 
exchanger and ions of the media in which the exchanger is immersed.  In the case of an 
insoluble anionic matrix, containing exchangeable cations, and a solution that contains 
cations, available for exchange, the reaction can be written as:  
++-++- +fi+ ABMBAM                                                                                       (1) 
where -M  is the negatively charged insoluble matrix, A+ and B+ are exchangeable 
cations, and barred symbols represent the solid phase.38  
 The properties of any ion-exchange material can be described in capacity and 
selectivity terms.39-40 
 The measurements of uptake values c or distribution coefficients KD can 
characterize the capacity of ion-exchange material that illustrates the amount of ions that 
can be replaced in the unit mass of solid.  
Uptake c may be expressed as:  
zm
VCCc finin )( -=                                                                                                            (2) 
where Cin and Cfin are concentrations of B+ solution before and after ion-exchange, m is 
mass of the dry sample, z ? charge of the cation  and V is aliquot volume of the solution. 
 KD might be calculated as: 
 15 
B
B
D C
CK =                                                                                                                           (3) 
where CB is the concentration of B+ in solid phase (barred) and solution,  or  
m
V
C
CCK
fin
finin
D
)( -=                                                                                                          (4) 
The selectivity constant describes the affinity of material for exchange of the cation A+ 
over the B+:  
  
B
B
A
A
BA C
C
C
CK =
/                                                                                                                 (5) 
where CA and CB are concentrations of the cations A+ and B+, respectively (barred 
symbols represent the solids).   
 For organic resins, capacity and selectivity are controlled by synthetic and 
pretreatment conditions.  In general, the resin is based on the hydrocarbon matrix with 
introduced functional groups, whose nature and strength define the functionality of the 
material. The water content or swelling of the resin is inversely related to the degree of 
crosslinking in the hydrocarbon matrix and determines the capacity values.38 Due to the 
highly reproducible ion-exchange capacities (~2 meq/g of dry sample), and predictable 
properties, organic resins are one of the best-known methods today for conventional 
water purification as well as the special ultrapure water pretreatment in pharmaceutics, 
electronics, and other highly technological industries. It is also widely used in extraction 
metallurgy, medicine, and agriculture.38  
 There is no straightforward theory that clarifies the origin of selectivity of 
inorganic framework ion-exchange materials.  Size, charge, and magnitude of hydration 
 16 
energy of exchanged cations, charge distribution of the matrix, structural features, degree 
of solution loading are just several major issues that should be considered and combined 
in order to explain ion-exchange properties for every particular material. Arrangements of 
all factors are able to favor the formation of the inorganic exchange materials with up to 9 
meq/g uptake values (Na+ exchange in titanium silicates10) and high selectivity to chosen 
cations.  High resistance to temperature and radiation damage, and low cost of synthesis 
make inorganic ion-exchange materials highly competitive for the removal of 137Cs and 
90Sr isotopes.  
 
ION-EXCHANGE LAYERED AND THREE-DIMENSIONAL INORGANIC 
MATERIALS FOR SELECTIVE Cs+ AND Sr2+ UPTAKE 
 Many layered and framework compounds with remarkable selectivity for Cs+ or  
Sr2+ were tested under conditions relevant to nuclear waste.  Ammonium 
molybdophosphate (AMP) possesses a high capacity for Cs+, but its application in the 
highly basic media is limited.41  
 Potassium cobalt hexacyanoferrate, a three-dimensional compound with a cubic 
face-centered structure, belonging to the Prussian Blue family, was extensively studied 
due to the high uptake of Cs+ in the presence of interfering cations over the pH range of 1 
to 13.42,43 The framework is built out of iron atoms, that reside in corners and face centers 
of the unit cell, cobalt atoms, located at the edges, and exchangeable potassium cations 
occupying the body center.  Low thermal stability resulting in decomposition of the 
sorbent at temperatures above 240 ?C 44 has restricted the application of the material, and 
has driven the search for alternatives.  
 17 
 The structure of sodium nonatitanate Na4Ti9O20 nH2O is still not well-resolved.45 
This semicrystalline compound with promising ion-exchange properties has a layered 
structure with an interlayer distance that depends on the water content, and can be as 
large as 10.0 ?.46 Batch and column experiments in two waste simulants, that differ in the 
content of citric acid, Na4EDTA, iminodiacetic acid, sodium gluconate, and other 
complex-forming agents, demonstrated that sodium nonatitanate is applicable for ion-
exchange with an extremely high Kd for Sr2+ of 2.35 ? 105 mL/g at the volume to mass 
ratio of 200 and 3.96 ? 104 mL/g at volume to mass ratio of 1000 at waste solutions with 
no formation of complex occurring.47,48 
 The family of titanium silicates has been considered as the most promising 
sorbents for Cs+ and Sr2+ removal from nuclear waste for many years.  The structure of 
sodium titanium silicate Na2Ti2O3(SiO4) H2O (commercial product name IONSIV? IE-
911) belongs to the hexagonal space group P42/mcm.3,49,50 (Figure 1.6) The 
crystallographic data are given in the Table 1.2. It is a framework material constructed 
from Ti four-member group clusters bridged by silicate groups in the a and b directions, 
with channels formed along the c axis.  In every cluster titanium octahedra are pairwise 
edge-shared, with pairs rotated by 90?.  In addition to tunnels, where four Na+ cations are 
located, there are small framework cavities located perpendicular to the channels, also 
occupied by Na+ cations.  
 This material is selective to Cs+ with Kd values ranging from 581 mL/g to 870 
mL/g in different simulants.63,64 At a pH>12, measured uptake value for the protonated 
form is  ~1.9 meq/g, which corresponds only to 25% of the total calculated exchange  
 
 18 
 
 
 
 
Figure 1.6.  A view of the crystal structure of Na2Ti2O3(SiO4) H2O along the [001] 
direction.  Yellow squares depict TiO6 octahedra, orange - SiO4 tetrahedra, green balls ? 
Na+ cations. Four out of the total eight Na+ cations are located in the channels, the other 
four (on the silicate groups) ? in small cavities.  Copied from reference 50 with author?s 
permission.  
 19 
Table 1.2.  Crystallographic data for Na2Ti2O3(SiO4) H2O (TiSi-1), 
HM3Ti4O4(SiO4) H2O (TiSi-2) and Na2Nb2-x MxO6-x(OH)x?H2O (SOMS) 
Compound TiSi-1 TiSi-2 SOMS 
Crystal System tetragonal cubic monoclinic 
Space group P42/mcm (No. 132) P 43m (No. 215) C2/c (No.15) 
a (?) 7.8082(2) 7.7644(3) 16.940(3) 
b (?) 7.8082(2) 7.7644(3) 5.033(5) 
c (?) 11.9735(4) 7.7644(3) 16.466(3) 
a (?) 90 90 90 

 (?) 90 90 114.00 
g (?) 90 90 90 
Z 4 1 8 
R(F)  0.055 0.055 0.0629 
Rw 0.142 0.114 0.1606 
 
 
 
 
 
 
 
 
 
 
 
 20 
capacity of the H2Ti2O3(SiO4) H2O.  This phenomenon, as well as preferred selectivity to 
Cs+ relative to other alkaline cations, can be easily explained using coordination distances 
and ionic radius data for Cs+: only two out of four exchanged cations can occupy the 
tunnel simultaneously, but bond distances of coordinated Cs+ are very close to the sum of 
Cs+ and O2- ionic radii. At the same time Na+ can compete for ion-exchange selectivity in 
the mixed solutions, occupying framework cavity sites.48  
 For Sr2+ cation exchange, sodium titanium silicate possesses the highest observed 
in this family of the compounds KD values of ~3.0 ? 105 mL/g.  This high selectivity 
might be ascribed to the presence of Sr2+ as Sr(OH)+ in the strongly basic conditions of 
nuclear waste and possibility of Sr(OH)+ occupying both tunnel and cavity exchange 
sites. 
 The other member of the titanium silicate family, a compound with the structure 
of mineral pharmacosiderite type HM3Ti4O4(SiO4) H2O (M=K, Na), has a framework 
built similarly to that described above.10,50 All differences between these two related 
structures, and their ion-exchange properties can be ascribed to the cubic nature of 
pharmacosiderite and its space group. (Table 1.2)  Titanium clusters are connected now 
in all three directions equivalently, which produces a system of perpendicular channels, 
parallel to all three axes. Three potential ion-exchange sites are placed in the cube face 
centers and one in the cubic body center of the unit cell.  After Cs+ exchange, three face 
sites can be selectively filled with Cs+ cations and the body site remains in the protonated 
form (or occupied by smaller cations) due to the restricted space requirements.  KDCs in 
alkaline solutions is 15360 mL/g, which can be compared with KDRb - 6190 mL/g, KDK - 
2580 mL/g, and KDLi ? 630 mL/g. The distribution coefficients are summarized in the 
 21 
Table 1.3. Distribution coefficients for Sr2+, KDSr, of Na4Ti9O20 nH2O, 
Na2Ti2O3(SiO4) H2O, and HK3Ti4O4(SiO4) H2O64 in different HLNW simulants.  
KDSr, mL/g 
NCAW simulant *  101SY-Cs5 simulant ** Compound 
V:m = 200 V:m = 1000 V:m = 200 
Na4Ti9O20 nH2O 2.35 ? 105 3.96 ? 104 295 
Na2Ti2O3(SiO4) H2O 2.70 ? 105 2.26 ? 105 231 
HK3Ti4O4(SiO4) H2O 2.02 ? 105 5.00 ? 103 31 
 
* The composition of NCAW is restricted only to presence of 0.43 M Al3+, 5 ? 10-4 M 
Cs+, 0.12 M K+, 4.99 M Na+, 5 ? 10-5 M Rb+, 2.7 ? 10-7 Sr2+, 0.23 M carbonate, 0.09 M 
fluoride, 3.4 M hydroxide,  1.67 M nitrate, 0.43 M nitrite, 0.15 M sulfate, and 0.025 M 
phosphate.  
** In addition in 101SY-Cs5 present 4.2 ? 10-3 M Ca2+, 1.96 ? 10-4 M Fe3+, 4.2 ? 10-4 M 
Mo4+, 2.5 ? 10-4 M Ni2+, 5.0 ? 10-4 M Zn2+, 5.0 ? 10-3 M citric acid, 5.0 ? 10-3 M 
Na4EDTA, 0.031 M iminodiacetic acid, 2.5?10-4 M Na3 nitrilotriacetate, 0.013 M sodium 
gluconate.  
 
 
 
 
 
 22 
partially explain the preference of the structure for Cs+ in terms of its hydration energy, 
which is not high enough to deny the introduction of cations into the relatively small 
channels.10,50  Reported  Sr2+ selectivity for pharmacosiderite structure in HLNW 
simulants with different pH values and Cs+ content is lower than for other titanium 
silicates and titanates.47,48 The ion-exchange data were also measured in reference to the 
degree of the crystallinity of the material. Results revealed participation of both 
absorption and ion-exchange mechanisms in the separation of Sr2+.  
 Recently Sandia National Laboratory invented a new series of compounds named 
Sandia Octahedral Molecular Sieves (SOMS).51-54 They are sodium niobate-based 
framework materials with the general formula Na2Nb2-xMxO6-x(OH)x?H2O, where M 
could be Ti or Zr with x < 0.4. (Table 1.2)  Substitution of pentavalent Nb coordination 
octahedra with tetravalent Ti or Zr coordination octahedra plays the same role as a 
substitution of Si with Al in zeolite structures.  It creates an anionic charge within the 
matrix that must be balanced.  The overall structure consists of double chains of edge-
shared octahedra of NbO6 and TiO6 (ZrO6) extending along the b axis.  These chains are 
intersected with layers of edge-shared NaO6 octahedra and this structural interaction 
forms a negatively charged framework. The fragment of the structure is depicted in the 
Figure 1.7.  There are two different sorts of Na+ cations in this compound: framework Na 
octahedra that participate in the matrix formation and Na+ counter cations located in the 
channels that balance negative charge of the matrix.  These latter cations are 
exchangeable.  
 
 
 23 
 
 
 
 
 
 
Figure 1.7.  This fragment depicts interconnection of octahedral units in the structure of 
Na2Nb2-xTixO6-x(OH)x?H2O.  Blue polyhedra represent disordered NbO6 and TiO6 
octahedra. Yellow polyhedra are Na coordination spheres, participating in the framework.  
Copied from reference 52 with author?s permission. 
 24 
 SOMS materials demonstrate exceptional selectivity toward all alkaline-earth 
cations relative to alkali metal cations For instance, the KD value of SOMS-1  
(Nb:Ti ratio is 4:1) in Na form for Ba2+, Sr2+, and Mg2+ are all above 99800 mL/g , but 
the KD values for Li+, K+, and Cs+ do not exceed 150 mL/g.  Upon heating they have one-
step phase transformation to perovskite type sodium niobate NaNbO3 without any 
intermediate stages like amorphization or decomposition.  Measured enthalpies of 
formation of hydrated, dehydrated, and dense forms of materials proved that dense 
perovskite structure is more thermodynamically favorable and may serve as a permanent 
ceramic host phase for the storage of 90Sr.51-54  
 
MAIN GROUP AND TRANSITION METAL PHOSPHATES  
 There have been countless remarkable catalysts,55-58 ion-exchangers,59,60 
conductors60 and many other materials with other applications in the area of various main 
group and transition metal phosphates.61 Along with useful properties, they display 
extraordinary structural diversity.  For instance, among aluminum phosphates alone there 
are more than 40 different framework types.  One eminent example is aluminophosphate 
VPI-5, which contains 18-membered ring channels with a diameter of 13 ?.62  
 Vanadium phosphates, including (VO)2P2O7, NaVOPO4, CaV2(P2O7),63 VOPO4? 
2H2O, VOHPO4?0.5H2O, VO(H2PO4)256 and others, represent, probably, the largest group 
of catalysts within one class of compounds.  Vanadyl pyrophosphate (VO)2P2O7, for 
example, is currently used in industry for the oxidation of butane to maleic anhydride. Its 
structure consist of the double chains of edge-sharing VO6 octahedra, interconnected by 
pyrophosphate groups into the framework.64 These pairs of VO6 octahedra are associated 
 25 
with active sites, where dehydrogenation of butane occurs.65 Other authors66 address the 
high oxidation activity of (VO)2P2O7 and other vanadium phosphate catalysts to the 
presence of  V=O double bonds at the active VO6 sites and the ability of oxygen from 
V=O to attack the reactants leading to the oxidative hydrogenation reaction.  
 In contrast, the group of nickel phosphates illustrates the extraordinary flexibility 
of their properties in this small group of compounds.  Two 24-membered ring framework 
compounds Ni18(HPO4)14(OH)3F9(H3O+,NH4+)4?12H2O (VSB-1)57 and 
Ni20[(OH)12(H2O)6][(HPO4)8(PO4)4]?12H2O (VSB-5)58 demonstrate a variety of 
properties. VSB-1 exhibits ion-exchange properties, antiferromagnetic ordering at 10 K 
and thermal stability up to temperatures above 550 ?C, as well as shape-selective catalytic 
activity in the hydroxylation of phenol.67 VSB-5 also possesses good temperature 
resistance and antiferromagnetic ordering.58 It also might serve as a hydrogenation 
catalyst upon calcination due to the availability of Ni sites, and as hydrogen storage 
material.68    
 The ion-exchange properties of layered transition metal phosphates 
Ti(HPO4)2?H2O, Zr(HPO4)2?H2O, Hf(HPO4)2?H2O, Ge(HPO4)2?H2O, Sn(HPO4)2?H2O, and 
Pb(HPO4)2?H2O are well characterized.59 The interlayer spacing, ranging between 7.56 ? 
and 7.8 ?, is confined by the oxygen atoms of the phosphate groups, which could be 
protonated. As a consequence, the ion-exchange properties of these compounds depend 
strongly on the pH, and reveal the maximal ion-exchange capacities between 4.17 meq/g 
for Hf(HPO4)2?H2O and 7.76 meq/g for Ti(HPO4)2?H2O in strongly basic conditions.  
 The other titanium phosphate, potassium titanyl phosphate KTiOPO4 (KTP) is 
one of the best known nonlinear optical materials.69  The cause of frequency doubling 
 26 
properties lies in the overall polarity of the structure, consisting of chains of highly 
distorted corner-sharing TiO6 octahedra, connected by phosphate tetrahedra.  
 As a summary of this short review and many other main group or transition metal 
phosphates not mentioned above, one can conclude that the presence of metal centers in 
these compounds are the source of their diverse properties.  We anticipate that the 
addition of the main group or transition metal centers in uranyl phosphate structures 
could also enrich their properties and could make uranyl-containing materials potentially 
applicable. 
 
 
 27 
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 32
CHAPTER 2 
CRYSTAL CHEMISTRY AND ION-EXCHANGE PROPERTIES OF THE 
LAYERED POTASSIUM URANYL IODATE, K[UO
2
(IO
3
)
3
]  
 
ABSTRACT 
Single crystals of potassium uranyl iodate, K[UO
2
(IO
3
)
3
] (KUI), were grown 
under mild hydrothermal conditions.  The structure of KUI contains two-dimensional 
2
?
[UO
2
(IO
3
)
3
]
1?
 sheets extending in the [ab] plane that consist of approximately linear 
UO
2
2+
 cations bound by iodate anions to yield UO
7
 pentagonal bipyramids.  There are 
three crystallographically unique iodate anions, two of which bridge between uranyl 
cations to create sheets, and one that is monodentate and protrudes in between the layers 
in cavities.  K
+
 cations have long ionic contacts with oxygen atoms from the layers 
forming an eight-coordinate distorted dodecahedral geometry.  These cations join the 
2
?
[UO
2
(IO
3
)
3
]
1?
 sheets together.  Ion-exchange reactions were carried out that indicate the 
selective uptake of Cs
+
 over Na
+
 or K
+
 by KUI.  Crystallographic data (193 K, MoK?, ? 
= 0.71073 ?): KUI, orthorhombic, Pbca, a = 11.495(1) ?, b = 7.2293(7) ?, c = 
25.394(2) ?, Z = 8, R(F) = 1.95% for 146 parameters with 2619 reflections with I > 
2?(I).  
 33
INTRODUCTION 
 Uranyl iodates have been known since at least the early 1900s with the correct 
composition of UO
2
(IO
3
)
2
(H
2
O) being reported in 1913.
1
 The precipitation of uranyl 
iodate as its hydrate has been used as a method of quantifying uranium for almost fifty 
years.
2,3
 The speciation of uranyl iodates in solution and subsequent precipitation has also 
been implicated in the fate of 
129
I (t
1/2
 = 1.7 x 10
7
 y), a key fission product in spent 
nuclear fuel.
4
  UO
2
(IO
3
)
2
(H
2
O) was also used as an early probe of the effects of radiation 
damage on uranium-bearing materials.
5
  Despite the importance of iodate in uranyl 
chemistry, the solid-state structure of a uranyl iodate was not known until Weigel and 
Engelhardt reported that UO
2
(IO
3
)
2
(H
2
O) was isostructural with UO
2
(BrO
3
)
2
(H
2
O), the 
latter structure being identified by X-ray powder diffraction methods.
6
   
In recent years uranyl iodates have been a rapidly expanding group of compounds 
prepared via hydrothermal conditions, whose structures are dominated by the formation 
of one-dimensional topologies.  These one-dimensional structures are known for 
relatively simple compounds such as UO
2
(IO
3
)
2
,
7
 as well as for materials that incorporate 
a diverse set of ligands e.g. Cs
2
[(UO
2
)
3
Cl
2
(IO
3
)(OH)O
2
]?2H
2
O,
8
 
Rb[(UO
2
)(CrO
4
)(IO
3
)(H
2
O)],
9
 and A
2
[(UO
2
)(MO
4
)(IO
3
)
2
] (A = K, Rb, Cs; M = Cr, 
Mo).
9,10
  Unidimensional features occur in additional uranyl iodates that incorporate ?
3
-
oxo atoms such as A
2
[(UO
2
)
3
(IO
3
)
4
O
2
] (A = K, Rb, Tl) and AE[(UO
2
)
2
(IO
3
)
2
O
2
] (AE = 
Sr, Ba, Pb),
11,12
 and in complex low-symmetry compounds like 
K
3
[(UO
2
)
2
(IO
3
)
6
](IO
3
)?H
2
O.
13
  Two-dimensional structures are less common, but are 
known for UO
2
(IO
3
)
2
(H
2
O)
6,7
 and Ag
4
(UO
2
)
4
(IO
3
)
2
(IO
4
)
2
O
2
.
14 
  One of the key features of 
the uranyl iodate system is the presence of a stereochemically active lone-pair of 
 34
electrons on the I(V) center.  The nonbonding nature of these electron pairs can cause the 
loss of a second dimension of connectivity, thereby leading to the formation of one-
dimensional topologies that are in some cases seemingly excised from previously known 
two-dimensional compounds.
11,12
  These lone-pairs also have the ability to align in the 
solid-state to create polar structures, albeit this is rare in uranyl compounds because the 
approximately linear uranyl cations often reside on, or are related by, centers of inversion 
or higher symmetry.  In fact, all uranyl iodates known to date are centrosymmetric.  If the 
discussion is expanded to include compounds containing NpO
2
+
, NpO
2
2+
, and PuO
2
2+
, 
then three actinyl iodates are known to form polar structures, NpO
2
(IO
3
), 
18
 
NpO
2
(IO
3
)
2
?H
2
O,
19
 and PuO
2
(IO
3
)
2
?H
2
O,
20
 all of which crystallize in the polar space 
group Pna2
1
.  If the composition is allowed to diverge further by considering all uranyl 
compounds with anions containing nonbonding electrons, then a few other acentric 
structures can be identified for PbUO
2
(SeO
3
)
2
 
21
  and Na
8
(UO
2
)
6
(TeO
3
)
10
.
22
  Members of 
the uranyl family of compounds with oxoanions of Sb(III) and Bi(III) are thus far found 
to be centrosymmetric.
23,24
  Channels can also be created to house the lone-pair of 
electrons in these types of compounds, which occurs in ?-AgNpO
2
(SeO
3
).
18
  Herein we 
report the preparation, crystal structure, and ion-exchange properties of a new layered 
uranyl iodate, K[UO
2
(IO
3
)
3
] (KUI).          
 
EXPERIMENTAL 
 Syntheses.  UO
3
 (99.8%, Alfa-Aesar), H
5
IO
6
 (99%, Alfa-Aesar), NaOH (97%, 
Aldrich), NaCl (99.99%, Aldrich), KOH (85.8%, Fisher), KCl (99%, Aldrich), K
2
CO
3
 
(99%, Aldrich), CsCl (99.9%, Aldrich), CsOH (99.9%, Aldrich) and V
2
O
5
 (99.95%, Alfa-
 35
Aesar) were used as received.  Distilled and Millipore filtered water with a resistance of 
18.2 M??cm was used in all reactions.  Reactions were run in Parr 4749 23-mL 
autoclaves with PTFE liners.  Accumet Basic AB 15 pH-meter was used for 
potentiometric measurements.  SEM/electron dispersive analysis by X-ray (EDX) 
analyses were performed using a JEOL 840/Link Isis instrument.  K, U, and I percentages 
were calibrated against standards.  Typical results were surprisingly good and are within 
1% of ratios determined from single crystal X-ray diffraction.  Warning: While the UO
3
 
contains depleted U, standard precautions for handling radioactive materials should be 
followed.        
 K[UO
2
(IO
3
)
3
].  UO
3
 (0.269 g, 0.940 mmol), K
2
CO
3
 (0.130 g, 0.940 mmol), V
2
O
5 
(0.171 g, 0.940 mmol), H
5
IO
6 
(0.429 g, 1.88 mmol), and 1.5 mL of deionized water were 
loaded into the 23 mL autoclave. The pH of the initial mixture was 1.1.  The autoclave 
was heated to 180 ?C in a box furnace for 72 h, and cooled at a rate of 9 ?C/h to room 
temperature.  The product mixture consisted of a colorless solution with a pH of 2.9 over 
a bright yellow precipitate containing tablets of KUI.  The product was washed with 
methanol and allowed to dry.  Crystals were separated from the mixture for further study.  
Yield 0.26 g (33% yield based on the U).  EDX analysis provided K:U:I ratio of 1:1:3 
(21%:19%:60%).  IR (KBr, cm
?1
): 902 (?
3,
 UO
2
2+
), 857 (?
1
,
 
UO
2
2+
), 832 (?,
 
IO
3
?
), 817 (?,
 
IO
3
?
), 808 (?,
 
IO
3
?
), 786 (?,
 
IO
3
?
), 763 (?,
 
IO
3
?
), 733 (?,
 
IO
3
?
), 525 (?, IO
3
?
).   
 Crystallographic Studies.  A tablet of KUI with dimensions of 0.133 x 0.046 x 
0.013 mm was mounted on a thin glass fiber with epoxy, secured on a goniometer head, 
cooled to ?80 ?C with an Oxford Cryostat, and optically aligned on a Bruker SMART 
APEX CCD X-ray diffractometer using a digital camera.  Intensity measurements were 
 36
performed using graphite monochromated Mo-K? radiation from a sealed tube with a 
monocapillary collimator.  SMART was used for preliminary determination of the cell 
parameters and data collection control.  The intensities of reflections of a sphere were 
collected by a combination of 3 sets of exposures (frames).  Each set had a different ? 
angle for the crystal and each exposure covered a range of 0.3? in ?.  A total of 1800 
frames were collected with an exposure time per frame of 30 s.   
 Determination of integrated intensities and global cell refinement were performed 
with the Bruker SAINT (v 6.02) software package using a narrow-frame integration 
algorithm.  An analytical absorption correction
25
 was applied followed by a semi-
empirical absorption correction using SADABS.
26
  The program suite SHELXTL (v 
6.12) was used for space group determination (XPREP), structure solution (XS), and 
refinement (XL).
25
  The final refinement included anisotropic displacement parameters 
for all atoms and a secondary extinction parameter.  Additional crystallographic details 
are listed in Table 2.1.  Atomic coordinates and equivalent isotropic displacement 
parameters are given in Table 2.2. 
 Ion-exchange studies.  0.01 M NaCl, 0.01 M KCl, and 0.01 M CsCl solutions 
were used for the study of the ion-exchange properties of KUI for Na
+
, K
+
, and Cs
+ 
ions, 
respectively. All samples were equilibrated in the solutions for three days The 
concentrations of the solutions before and after uptake were measured with ion-selective 
electrodes.
27
  The mass to volume ratio was 1:1000 (0.01 g for 10 ml of solution).   
 
 
 
 37
Table 2.1.  Crystallographic data for K[UO
2
(IO
3
)
3
] (KUI). 
Compound KUI 
Formula mass  833.83 
Color and habit yellow tablet 
Crystal system orthorhombic 
Space group  Pbca (No. 61) 
a (?) 11.495(1) 
b (?) 7.2293(7) 
c (?) 25.394(2) 
? (
o
) 90 
? (
o
) 90 
? (
o
) 90 
V (?
3
) 2110.3(3) 
Z 8 
T (?C) 
193 K 
? (?) 
0.71073 
2?
max
 56.64 
?
calcd
 (g cm
?3
) 
5.249 
?(Mo K?) (cm
?1
) 
246.03 
R(F) for F
o
2
 > 2?(F
o
2
) 
a
 
0.0195 
R
w
(F
o
2
) 
b
 0.0458 
a
 
()
RF F F F=???
oc o
.  
b
 
() ( )
RF wF F wF
wo
2
o
2
c
2
2
o
4
12
=?
?
?
?
?
?
?
??
?
?
?
?
?
?
.  
 
 38
Table 2.2.  Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 
K[UO
2
(IO
3
)
3
] (KUI). 
Atom Symmetry
a
 x y z U
eq
 (?
2
) 
a
 Occup. 
U(1) 8   c   1 0.0255(1)     0.0351(1) 0.6519(1) 0.009(1) 1 
I(1) 8   c   1 0.0654(1)     0.4563(1) 0.5630(1) 0.013(1) 1 
I(2) 8   c   1 -0.2992(1)    0.1366(1) 0.6557(1) 0.011(1) 1 
I(3) 8   c   1 0.3409(1)     0.0593(1) 0.7031(1) 0.010(1) 1 
K(1) 8   c   1 0.1642(1)     -0.9480(2) 0.4781(1) 0.026(1) 1 
O(1) 8   c   1 0.0605(3)     0.3375(4) 0.6280(1) 0.012(1) 1 
O(2) 8   c   1 -0.0357(3)    0.3232(5) 0.5246(1) 0.018(1) 1 
O(3) 8   c   1 0.1980(3)     0.3599(5) 0.5391(1) 0.021(1) 1 
O(4) 8   c   1 -0.1523(3)    0.2142(5) 0.6423(1) 0.016(1) 1 
O(5) 8   c   1 -0.3464(3)    0.1100(5) 0.5888(1) 0.019(1) 1 
O(6) 8   c   1 -0.3497(3)    0.3740(4) 0.6669(2) 0.017(1) 1 
O(7) 8   c   1 0.2277(3)     0.0367(5) 0.6539(1) 0.014(1) 1 
O(8) 8   c   1 0.2723(3)     0.2224(5) 0.7463(1) 0.016(1) 1 
O(9) 8   c   1 0.4362(3)     0.2138(4) 0.6671(1) 0.014(1) 1 
O(10) 8   c   1 0.0261(3)     0.0927(5) 0.7202(1) 0.015(1) 1 
O(11) 8   c   1 0.0272(3)     -0.0278(4) 0.5842(1) 0.014(1) 1 
a
 Symmetry describes multiplicity, Wyckoff parameter and symmetry of the atomic site. 
b
 U
eq 
is defined as one-third of the trace of the orthogonalized U
ij
 tensor. 
 
 
 
 39
RESULTS AND DISCUSSION  
Syntheses.  The reaction of UO
3
 with KIO
4
 and V
2
O
5
 under mild basic 
hydrothermal conditions has been previously shown to result in the formation of 
K
2
[(UO
2
)
2
(VO)
2
(IO
6
)
2
O]?H
2
O in high yield.
28
  In an effort to explore both the 
compositional space of this reaction and the effects of pH on product formation we have 
continued to investigate this reaction.  In acidic conditions K[UO
2
(IO
3
)
3
] (KUI) is 
formed in moderate yield from similar reactants (K
2
CO
3
 and H
5
IO
6
 instead of KIO
4
) that 
yielded K
2
[(UO
2
)
2
(VO)
2
(IO
6
)
2
O]?H
2
O.   
Structure.  K[UO
2
(IO
3
)
3
].  The structure of KUI consists of an approximately linear 
UO
2
2+
 cation with U=O distances of 1.777(3) and 1.785(3) ? and an O=U=O angle of 
178.39(15)?. (Table 2.3)  This moiety is bound by five iodate anions to form a pentagonal 
bipyramidal coordination environment around the uranium center as is depicted in Figure 
2.1.  A similar building unit also occurs in one-dimensional K
3
[(UO
2
)
2
(IO
3
)
6
](IO
3
)?H
2
O,
13
 
although the overall connectivity and dimensionality is different from KUI.  The U?O 
bond distances in the equatorial plane range from 2.304(3) to 2.432(3) ?.  These oxygen 
atoms are approximately planar and deviate from planarity by only approximately 0.08 ?.  
There are three crystallographically unique iodate anions in KUI.  Two of these anions 
bridge between two uranyl cations and have one terminal oxygen atom.  The bridging 
versus terminal I?O bond distances can be differentiated with bridging distances 
occurring from 1.811(3) to 1.834(3) ?, whereas the terminal I?O distances are both 
shorter at 1.793(3) ?.  The third iodate anion is monodentate and has a bridging I?O 
distance of 1.862(3) ?, and two terminal distances of 1.782(3) and 1.796(3) ?. 
 
 40
Table 2.3.  Selected Bond Distances (?) and Angles (?) for K[UO
2
(IO
3
)
3
] (KUI).  
Bond Lengths (?) 
U(1)?O(1) 2.304(3) I(1)?O(2) 1.796(3) 
U(1)?O(4) 2.432(3) I(1)?O(3) 1.782(3) 
U(1)?O(6) 2.363(3) I(2)?O(4) 1.812(3) 
U(1)?O(7) 2.325(3) I(2)?O(5) 1.793(3) 
U(1)?O(9) 2.396(3) I(2)?O(6) 1.834(3) 
U(1)?O(10) 1.785(3) I(3)?O(7) 1.811(3) 
U(1)?O(11) 1.777(3) I(3)?O(8) 1.793(3) 
I(1)?O(1) 1.862(3) I(3)?O(9) 1.812(3) 
Angles (?) 
O(10)?U(1)?O(11) 178.39(15) O(5)?I(2)?O(6) 98.72(16) 
O(3)?I(1)?O(11) 99.18(17) O(4)?I(2)?O(6) 91.97(15) 
O(3)?U(1)?O(1) 98.46(15) O(8)?I(3)?O(7) 99.50(15) 
O(2)?I(1)?O(1) 102.40(15) O(8)?I(3)?O(9) 99.77(15) 
O(5)?I(2)?O(4) 97.84(16) O(7)?I(3)?O(9) 98.19(15) 
 
 
 
 
 
 
 
 41
 
 
 
 
 
Figure 2.1.  A view of the pentagonal bipyramidal coordination environment around 
uranium center in KUI that is formed from a UO
2
2+
 linear cation connected with five 
iodate groups through the equatorial plane.   
 42
The bridging of the uranyl cations by the iodate anions creates two-dimensional 
sheets in the [ab] plane as shown in Figure 2.2.  From this perspective it appears that the 
monodentate iodate anions reside in cavities within the layers.  In fact, a view along the b 
axis (Figure 1.3) shows that these iodate anions protrudes in between the layers and 
provides their terminal oxo atoms for forming interactions with the K
+
 cations.  The 
interactions between the K
+
 cations and iodate anions stitch the structure together.  The 
K
+
 cations form long interactions with the terminal oxo atoms from both the monodentate 
iodate group as well as with the terminal oxo atoms from one of the bridging iodate 
anions.  These cations also interact with the oxo atoms from the uranyl cations forming a 
surprisingly short contact of 2.715(3) ?.
34-39
 A total of eight K
+
???O contacts are formed, 
with distances ranging from 2.615(4) to 3.175(4) ?, creating a distorted dodecahedral 
environment around the potassium centers. 
 Ion-exchange Studies.  The exchange of interlayer cations has been previously 
achieved in a number of layered uranyl compounds, most notably in the autunite and 
meta-autunite group.
40-42
  In addition, certain uranyl compounds such as hydrogen uranyl 
phosphate (HUP)
43-46
 and Cs
4
[(UO
2
)
2
(V
2
O
7
)O
2
]
47
 have been shown to exhibit high 
cationic conductivities.  In order to evaluate the potential for ion-exchange reactions of 
alkali metal cations with KUI, samples were equilibrated with 0.01 M solutions of NaCl, 
KCl, or CsCl.  The potential ion exchange of K
+
 with Na
+
 or Cs
+
 was measured 
potentiometrically using ion-selective electrodes.  In order to distinguish between 
absorption and actual ion exchange, the release of K
+
 was also quantified.  No 
measurable exchange was noted with Na
+
.  Similarly, there was also no change noted in  
 
 43
 
 
 
 
 
 
 
 
 
 
Figure 2.2. An illustration of the 
2
?
[UO
2
(IO
3
)
3
]
1?
 sheets in KUI that extend in the [ab] 
plane.    
 44
 
 
 
 
 
 
 
 
 
 
 
Figure 2.3. A view along the b axis of KUI showing that the monodentate iodate anion 
protrudes in between the layers, providing its terminal oxo atoms for forming interactions 
with the K
+
 cations that reside between the layers. 
 45
the concentration of K
+
 in solution in K
+
 self-exchange reactions, which does not 
discount the possibility that equilibrium is established and exchange takes places.  
However, substantial Cs
+
 ion exchange was noted with high uptake values of up to 
3.7(1.2) meq/g.  The Cs
+
 ionophore is 2.53 orders of magnitude more selective for Cs
+
 
than K
+
.  Therefore, the Cs
+
 uptake value probably overestimates Cs
+
 exchange because 
some K
+
 is simultaneously being detected.  In order to address this issue we also 
measured the release of K
+
 back into solution and found a large value of 1.7 meq/g.  This 
determination demonstrates that ion exchange is actually taking place.  The resultant 
solids were examined using EDX, and these measurements demonstrate complete 
exchange of K
+
 for Cs
+
 with no measurable amount of K
+
 being observed in the ion-
exchanged solid.  Given that the reaction takes place at room temperature in basic media, 
and that uranyl iodates are extremely insoluble in water even at low pH, we suggest that 
dissolution and recrystallization do not occur concomitantly with the exchange process.  
In order to confirm this, powder X-ray diffraction data were collected before and after ion 
exchange.  The diffraction patterns were superimposable, indicating that there is virtually 
no structural change that occurs concomitantly with ion exchange.   
 
CONCLUSIONS 
 The uranyl iodate system continues to provide remarkable new structure types 
unparalleled by other types of oxoanions.  The formation of K[UO
2
(IO
3
)
3
] under less 
acidic conditions (final pH = 2.9 vs. ca. 1) than have been typically employed in the past 
to prepare uranyl iodates may point to a new family of compounds that form at higher 
pH.  Studies to address this issue are underway.  We note that attempts to prepare 
 46
Cs[UO
2
(IO
3
)
3
] directly under conditions equivalent to those used to prepare KUI failed.  
Instead a new polycrystalline phase forms with a Cs/U/I ratio of 1:3:1.  We have been 
unable as yet to determine the structure of this new cesium uranyl iodate.  This result 
suggests that the K
+
 cations play a structure-directing role in the formation of KUI.        
 
 47
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State Chem. 2004, 177, 725. 
14. Bean, A. C.; Campana, C. F.; Kwon, O.; Albrecht-Schmitt, T. E. J. Am. Chem. Soc. 
2001, 123, 8806. 
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18. Albrecht-Schmitt, T. E.; Almond, P. M.; Sykora, R. E. Inorg. Chem. 2003, 42, 3788. 
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A. C.; Scott, B. L.; Albrecht-Schmitt, T. E. ; Runde, W. Inorg. Chem. 2003, 42, 
5632. 
20. Runde, W.; Bean, A. C.; Albrecht-Schmitt, T. E.; Scott, B. L. Chem. Commun. 
(Cambridge) 2003, 4, 478. 
21. Almond, P. M.; Albrecht-Schmitt, T. E. Inorg. Chem. 2002, 41, 1177. 
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2004,  177,  1717 
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Refining, and Displaying Crystal Structures from Diffraction Data; Siemens 
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Moffatt, A. Am. Mineral. 1998, 83, 390. 
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32. Brown, I. D.;  Altermatt, D. Acta Crystallogr. 1985, B41, 244. 
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 50 
CHAPTER 3 
SYNTHESES, STRUCTURES, AND ION-EXCHANGE PROPERTIES OF THE 
THREE-DIMENSIONAL FRAMEWORK URANYL GALLIUM PHOSPHATES, 
Cs4[(UO2)2(GaOH)2(PO4)4]?H2O AND Cs[UO2Ga (PO4)2] 
 
ABSTRACT 
The reaction of UO2(NO3)2?6H2O with Cs2CO3 or CsCl, H3PO4, and Ga2O3 under 
mild hydrothermal conditions results in the formation of Cs4[(UO2)2(GaOH)2(PO4)4]?H2O 
(UGaP1) or Cs[UO2Ga(PO4)2] (UGaP2).  The structure of UGaP1 was solved from a 
twinned crystal revealing a three-dimensional framework structure consisting of one-
dimensional 1? [Ga(OH)(PO4)2]4? chains composed of corner-sharing GaO6 octahedra and 
bridging PO4 tetrahedra that extend along the c axis.  The phosphate anions bind the 
UO22+ cations to form UO7 pentagonal bipyramids.  The UO7 moieties edge-share to 
create dimers that link the gallium phosphate substructure into a three-dimensional 
3
? [(UO2)2(GaOH)2(PO4)4]
4? anionic lattice that has intersecting channels running down 
the b and c axes.  Cs+ cations and water molecules occupy these channels.  The structure 
of UGaP2 is also three-dimensional and contains one-dimensional 1? [Ga(PO4)2]3? gallium 
phosphate chains that extend down the a axis.  These chains are formed from fused eight-
membered rings of corner-sharing GaO4 and PO4 tetrahedra.  The chains are in turn 
linked together into a three-dimensional 3? [UO2Ga(PO4)2]1? framework by edge-sharing 
 51 
UO7 dimers as occurs in UGaP1. There are channels that run down the a and b axes 
through the framework.  These channels contain the Cs+ cations.  Ion-exchange studies 
indicate that the Cs+ cations in UGaP1 and UGaP2 can be exchanged for Ca2+ and Ba2+.  
Crystallographic data: UGaP1, monoclinic, space group P21/c, a = 18.872(1), b = 
9.5105(7), c = 14.007(1) ?, 
 = 109.65(3), Z = 4 (T = 295 K); UGaP2, triclinic, space 
group P1, a = 7.7765(6), b = 8.5043(7), c = 8.9115(7) ?,  = 66.642(1), 
 = 70.563(1),  
= 84.003(2), Z = 2 (T = 193 K). 
 
INTRODUCTION 
The syntheses, structures, and physicochemical properties of gallium phosphates 
have been the subjects of intense interest for two decades owing to their enormously rich 
structural chemistry that is particularly well noted for forming microporous open-
framework topologies that in some cases are similar to the AlPO4 family of compounds.1-
4 The diversity in this class of compounds finds its origins in the fundamental 
coordination chemistry of Ga(III), which occurs as GaO4 tetrahedra (e.g. in 
[H3N(CH2)3NH3][GaH(PO4)2]5 and [Ga(HPO4)(PO4)(OH)]?[(C2H7N)3N]?H2O6), GaO5 
trigonal bipyramids (e.g. in [NH4][Ga(OH)(PO4)]7 and Ga3(PO4)3?C3H9N?H2O8), and 
GaO6 octahedra (e.g. in [NH4]3[Ga2(PO4)3]7 and Rb(GaPO4)2(OH)(H2O)?H2O9).  In fact, 
there are examples of compounds where Ga exhibits multiple geometries in the same 
compound as has been found for Na[Ga2(OH)(PO4)2]10 and 
Na3Ga5(PO4)4O2(OH)2?2H2O,11 which contain GaO5 trigonal bipyramids and GaO6 
octahedra.  These fundamental building units can combine with phosphate tetrahedra in a vast 
number of permutations to create zero-dimensional structures in 
 52 
[Ga(HPO4)(PO4)(OH)]?[(C2H7N)3N]?H2O6 and [C6H5NH]2[H8Ga4P4O21],12 one-dimensional 
chains as found in the organically templated gallium phosphates 
[NH3(CH2)4NH3][Ga(PO4)(PO3OH)],13 [(1R,2R)-C6H10(NH3)2][Ga(OH)(HPO4)2]?H2O,14 and 
[NH3(CH2)2(NH3)][Ga(H2PO4)(P2O7)],15 two-dimensional sheets in [C5H6N][Ga(HPO4)2(H2O)2]16 
and [NH4]Ga(OH)(PO4)],7 and three-dimensional networks in NaGa2(OH)(PO4)2,10 
Na3Ga5(PO4)4O2(OH)2?2H2O,11 and [NH3(CH2)3(NH3)][Ga3(PO4)3(H2O)].17   
The structural complexity and properties of gallium phosphates can be expanded 
through the inclusion of transition metals into the anionic lattice.  The incorporation of 
transition metals into gallium phosphates can take place in several ways.  First, partial 
substitution at Ga sites can take place to yield disordered compounds, which is illustrated 
by [C5H5NH][CoGa2P3O12], where CoO4/GaO4 disorder exists.18  Anomalous X-ray 
scattering is a powerful tool in this regard, and has been used to establish the distribution 
of Zn2+ and Ga3+ in a series of zinc-substituted gallium phosphates.19  Second, the 
transition metal centers can force the adoptions of new structure types to accommodate 
additional building units as occurs in Rb[(VO)(H2O)Ga(PO4)2]20 and 
Mn3(H2O)6Ga4(PO4)6,21 the latter of which forms gallium phosphate channels to house 
Mn3(H2O)6O8 clusters.  This compound also exhibits superexchange interactions between 
Mn(II) centers, illustrating one of the many properties that can be added to gallium 
phosphates by incorporating transition metals.21  
In order to prepare uranyl compounds with three-dimensional open-framework 
structures, we have focused on the use of octahedral anions, such as periodate, IO65?, as 
building units.22,23  The formation of three-dimensional network structures incorporating 
the approximately linear uranyl, UO22+, cation are not common because uranyl-
 53 
containing polyhedra typically condense with uranyl units parallel to one another, and 
because the uranyl oxo atoms are typically terminal, layered structures most often 
result.24  In spite of this structural propensity, a number of different uranyl systems have 
been shown to adopt three-dimensional framework structures including phosphates such 
as [C4H12N2](UO2)[(UO2)(PO4)]4?2H2O25 and [(UO2)3(PO4)O(OH)(H2O)2](H2O),26 the 
fluorophosphate [C6H14N2]2[(UO2)6(H2O)2F2(PO4)2(HPO4)4]?4H2O,27 arsenates, e.g. 
[NH(C2H5)3][(UO2)2(AsO4)(AsO3OH)],25 vanadates, e.g. A(UO2)4(VO4)3 (A = Li, Na),28 
and oxides, e.g. (NH4)3(H2O)2{[(UO2)10O10(OH)][(UO4)(H2O)2]}.29  In this chapter we 
report the preparation and characterization of the first examples of actinide-containing 
gallium phosphates, Cs4[(UO2)2(GaOH)2(PO4)4]?H2O (UGaP1) and Cs[UO2Ga(PO4)2] 
(UGaP2), both of which possess three-dimensional framework structures. 
 
EXPERIMENTAL 
 Syntheses.  UO2(NO3)2?6H2O (98%, Alfa-Aesar), Ga2O3 (99.99%, Alfa-Aesar), 
Cs2CO3 (99.99%, Alfa-Aesar), H3PO4 (98%, Aldrich), KCl (99%, Aldrich), NaCl (99%, 
Aldrich), CsCl (99.9%, Cerac), CaCl2 (99%, Aldrich), and BaCl2 (99%, Aldrich) were 
used as received. Reactions were performed in the PTFE-lined Parr 4749 autoclaves.  
Distilled and Millipore filtered water with a resistance of 18.2 M?cm was used in all 
reactions.  Standard precautions were performed for handling radioactive materials 
during work with UO2(NO3)2?6H2O and the products of the reactions.  Semi-quantitative 
SEM/EDX analyses were performed using a JEOL 840/Link Isis instrument.  Cs, U, Ga, 
and P percentages were calibrated against standards.            
 54 
Cs4[(UO2)2(GaOH)2(PO4)4](H2O) (UGaP1).  UO2(NO3)2?6H2O  (0.238 g, 0.474 
mmol), Ga2O3 (0.112 g, 0.948 mmol),  H3PO4 (0.186 g, 1.88 mmol),  Cs2CO3 (0.464 g, 
1.41 mmol), and 1 mL water were loaded into a 23 mL autoclave.  The autoclave was 
then heated to 180 ?C in a box furnace for 12 d and slow cooled at 3 ?C/h to room 
temperature.  The product mixture consisted of a colorless solution and a bright yellow 
precipitate.  The solid was washed with water and methanol and allowed to dry.  
Rectangular shape tablets of UGaP1 were then separated, with a yield of 130 mg (55% 
yield based on the U), from the mixture for further study.  The Cs:U:Ga:P ratio 
determined from EDX analysis was approximately 2:1:1:2. 
Cs[UO2Ga(PO4)2] (UGaP2).  UO2(NO3)2?6H2O  (0.307 g, 0.611 mmol), Ga2O3 
(0.144 g, 1.22 mmol), H3PO4 (0.239 g, 2.44 mmol), and CsCl (0.309 g, 1.83 mmol) were 
loaded into the 23 mL autoclave followed by the addition of 2 mL of water.  The 
autoclave was heated for 4 d at 180 ?C in a box furnace and then cooled to room 
temperature at 9 ?C/h.  The solid product consisted of a mixture of white and green-
yellow crystals. After decanting the mother liquor, the product was washed with water 
and methanol and allowed to dry.  Rectangular shape green-yellow tablets of UGaP-2 
were then separated from the mixture of yellow and white amorphous precipitates.  The 
isolated yield was 46 mg (15% yield based on the U).  EDX analysis provided Cs:U:Ga:P 
ratio of 1:1:1:2.     
Crystallographic Studies.  Crystals of Cs4[(UO2)2(GaOH)2(PO4)4]?H2O 
(UGaP1) and Cs[UO2Ga(PO4)2] (UGaP2) were mounted on glass fibers and aligned on a 
Bruker SMART APEX CCD X-ray diffractometer.  Intensity measurements were 
performed using graphite monochromated Mo Ka radiation from a sealed tube and 
 55 
monocapillary collimator.  SMART (v 5.624) was used for preliminary determination of 
the cell constants and data collection control.  The intensities of reflections of a sphere 
were collected by a combination of 3 sets of exposures (frames).  Each set had a different 
f angle for the crystal and each exposure covered a range of 0.3? in w.  A total of 1800 
frames were collected with an exposure time per frame of 30 s for UGaP1 and 120 s for 
UGaP2. 
Crystals of UGaP1 suffered from two problems.  First, the crystal cracked when 
cooled to 193 K, and the data was therefore collected at 295 K.  Second, all of the 
crystals examined proved to be twinned.  GEMINI was used to separated the individual 
components of the twin, and the structure was solved as follows. 
 For UGaP1 and UGaP2 determination of integrated intensities and global 
refinement were performed with the Bruker SAINT (v 6.02) software package using a 
narrow-frame integration algorithm.  A face-indexed analytical absorption correction was 
initially applied using XPREP, where individual shells of unmerged data were corrected 
analytically.30  These files were subsequently treated with a semiempirical absorption 
correction by SADABS.31  The program suite SHELXTL (v 6.12) was used for space 
group determination (XPREP), direct methods structure solution (XS), and least-squares 
refinement (XL).30  The final refinements included anisotropic displacement parameters 
for all atoms.  Secondary extinction was not noted for either crystal.  Some 
crystallographic details are given in Table 3.1. Atomic coordinates, symmetry, 
displacement  parameters and occupancy for UGaP1 and UGaP2 can be found in Tables 
3.2 and 3.3 respectively.     
 56 
Table 3.1. Crystallographic Data for Cs4[(UO2)2(GaOH)2(PO4)4]?H2O (UGaP1) and 
Cs[UO2Ga(PO4)2] (UGaP2). 
Formula Cs4[(UO2)2(GaOH)2(PO4)4]?H2O Cs[UO2Ga(PO4)2] 
Formula Mass 1641.04 662.60 
Color and habit yellow tablet yellow-green tablet 
Space group P21/c (No. 14)  P1 (No. 2) 
a (?) 18.872(1) 7.7765(6)  
b (?) 9.5105(7) 8.5043(7) 
c (?) 14.007(1) 8.9115(7) 
 (?) 90 66.642(1) 

 (?) 109.65(3) 70.563(1) 
 (?) 90 84.003(2) 
V (?3) 2367.5(3) 509.96(7) 
Z 4 2 
T (K) 295 193 
l (?) 0.71073 0.71073 
Maximum 2q (deg.) 56.64 56.60 
rcalcd (g cm?3) 4.598 4.315 
m(Mo Ka) (cm?1) 223.20 223.65 
R(F) for Fo2 > 2s(Fo2)  0.0424 0.0283 
Rw(Fo2) b 0.0973 0.0626 
a ( )R F F F F= -
 

o c o .  
b ( ) ( )R F w F F wF
w o
2
o
2
c
2 2
o
4
1 2
= - 
 
  . 
 
 57 
Table 3.2.  Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 
Cs4[(UO2)2(GaOH)2(PO4)4]?H2O (UGaP1) 
Atom Symmetrya x y z Ueq (?2) b Occup. 
U(1) 4  e 1 0.53831(2) -0.70597(4) 0.51964(3) 0.01196(9) 1 
U(2) 4  e 1 0.96212(2) -0.71325(4) 0.98701(3) 0.01205(9) 1 
Ga(1) 4  e 1 1.25499(6) -0.77386(9) 1.23126(8) 0.0119(2) 1 
Ga(2) 4  e 1 1.25230(6) -0.74603(9) 0.98122(8) 0.0116(2) 1 
P(1) 4  e 1 0.65190(15) -0.4630(3) 0.6033(2) 0.0125(5) 1 
P(2) 4  e 1 1.37577(14) -0.9350(3) 1.41044(19) 0.0114(5) 1 
P(3) 4  e 1 1.13089(14) -0.9361(3) 1.05030(19) 0.0119(5) 1 
P(4) 4  e 1 0.84790(14) -0.4578(3) 0.92909(19) 0.0121(5) 1 
O(1) 4  e 1 0.6951(4) -0.4196(8) 0.5334(6) 0.0191(16) 1 
O(2) 4  e 1 0.6759(4) -0.3792(8) 0.7011(5) 0.0214(17) 1 
O(3) 4  e 1 0.5646(4) -0.4485(8) 0.5480(6) 0.0201(16) 1 
O(4) 4  e 1 0.6597(4) -0.6228(8) 0.6239(6) 0.0194(16) 1 
O(5) 4  e 1 1.4520(4) -0.8644(8) 1.4320(6) 0.0221(17) 1 
O(6) 4  e 1 1.3367(4) -0.8782(8) 1.4808(5) 0.0189(16) 1 
O(7) 4  e 1 1.3898(4) -1.0935(7) 1.4311(6) 0.0191(16) 1 
O(8) 4  e 1 1.3282(4) -0.9177(7) 1.2987(5) 0.0171(16) 1 
O(9) 4  e 1 1.1138(4) -1.0931(8) 1.0239(5) 0.0167(15) 1 
O(10) 4  e 1 1.1620(4) -0.8683(7) 0.9734(5) 0.0157(15) 1 
O(11) 4  e 1 1.0566(4) -0.8644(8) 1.0469(6) 0.0207(16) 1 
O(12) 4  e 1 1.1873(4) -0.9266(7) 1.1595(5) 0.0132(14) 1 
O(13) 4  e 1 0.8396(4) -0.6171(7) 0.9056(5) 0.0160(15) 1 
O(14) 4  e 1 0.9351(4) -0.4443(8) 0.9846(6) 0.0193(16) 1 
O(15) 4  e 1 0.8051(4) -0.4207(7) 1.0013(6) 0.0186(16) 1 
 58 
O(16) 4  e 1 0.8234(4) -0.3690(7) 0.8332(5) 0.0158(15) 1 
O(17) 4  e 1 0.5129(4) -0.7187(7) 0.6326(5) 0.0203(16) 1 
O(18) 4  e 1 0.5646(4) -0.6883(8) 0.4085(5) 0.0204(16) 1 
O(19) 4  e 1 0.9609(4) -0.6969(7) 1.1141(6) 0.0205(16) 1 
O(20) 4  e 1 0.9633(4) -0.7357(8) 0.8610(5) 0.0183(16) 1 
O(21) 4  e 1 1.2074(4) -0.7272(7) 0.8361(5) 0.0143(15) 1 
O(22) 4  e 1 1.2998(4) -0.7656(7) 1.1254(5) 0.0139(14) 1 
O(23) 4  e 1 0.7509(7) -0.6656(13) 1.0535(10) 0.068(3) 1 
Cs(1) 4  e 1 0.70707(4) -0.81967(8) 0.83263(7) 0.0337(2) 1 
Cs(2) 4  e 1 0.55975(5) -0.47401(9) 0.80426(6) 0.03157(19) 1 
Cs(3) 4  e 1 0.83707(4) -0.60810(8) 0.67258(6) 0.02768(17) 1 
Cs(4) 4  e 1 0.93184(4) -0.45410(8) 1.23164(6) 0.02884(18) 1 
a Symmetry describes multiplicity, Wyckoff parameter and symmetry of the atomic site. 
b Ueq is defined as one-third of the trace of the orthogonalized Uij tensor. 
 59 
 Table 3.3.  Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 
Cs[UO2Ga(PO4)2] (UGaP2). 
Atom Symmetrya x y z Ueq (?2) b Occup. 
U(1) 2  i  1 0.21442(3) 0.92139(3) 0.33450(3) 0.00955(7) 1 
Ga(1) 2  i  1 0.24602(10) 0.57980(9) 0.98833(9) 0.01023(14) 1 
P(1) 2  i  1 -0.0413(2) 0.3270(2) 1.2841(2) 0.0103(3) 1 
P(2) 2  i  1 0.5302(2) 0.7365(2) 1.0581(2) 0.0099(3) 1 
O(1) 2  i  1 0.0560(6) 0.8460(6) 0.2720(6) 0.0159(10) 1 
O(2) 2  i  1 0.3671(7) 0.9913(6) 0.4080(6) 0.0145(9) 1 
O(3) 2  i  1 -0.2013(6) 0.3571(6) 0.0150(10) 0.0195(18) 1 
O(4) 2  i  1 0.0248(7) 0.1492(6) 1.3771(6) 0.0140(9) 1 
O(5) 2  i  1 -0.0888(6) 0.3241(6) 1.1313(6) 0.0137(9) 1 
O(6) 2  i  1 0.1153(7) 0.4610(6) 1.2133(6) 0.0158(10) 1 
O(7) 2  i  1 0.3828(7) 0.7476(6) 0.9725(6) 0.0153(10) 1 
O(8) 2  i  1 0.5978(6) 0.5503(6) 1.1144(6) 0.0131(9) 1 
O(9) 2  i  1 0.6848(7) 0.8614(6) 0.9304(6) 0.0156(10) 1 
O(10) 2  i  1 0.4475(6) 0.7700(6) 1.2225(6) 0.0141(9) 1 
Cs(1) 2  i  1 0.66307(6) 0.68745(6) 0.49084(6) 0.02003(11) 1 
a Symmetry describes multiplicity, Wyckoff parameter and symmetry of the atomic site. 
b Ueq is defined as one-third of the trace of the orthogonalized Uij tensor. 
 
 
 
 
 
 60 
Ion-exchange Studies.  An Accumet Basic AB 15 pH meter was used for 
potentiometric measurements.  The ion-exchange properties of UGaP1 and UGaP2 were 
evaluated to determine the uptake values of Na+, K+, Ca2+, and Ba2+ ions from NaCl, KCl, 
CaCl2, and BaCl2 solutions respectively in the range of the concentrations from 0.0001 M 
to 0.1 M.  The release values of Cs+ ions were also measured.  The concentrations of the 
solutions before and after uptake and release were determined using ion-selective 
electrodes.32  The volume to mass ratio was 200:1 (2 mL of the solution for 0.01 g of 
sample). 
Uptake of Sr2+ and duplicated measurements of Ca2+ concentrations were 
performed on a Varian 240 AA spectrometer with Hollow cathode Ca and Sr lamps. The 
volume to mass ratio in these experiments was 200:1 (4 mL of the solution for 0.02 g of 
sample). 
 Thermal analysis. DSC data were collected using differential scanning 
calorimeter TA Instrument, model. The samples of known mass encapsulated in 
aluminum container, were heated under nitrogen atmosphere from 30 ?C to 600 ?C with 
heating rate 10?C /minute.  
 
RESULTS AND DISCUSSION  
 Synthesis.  While the syntheses of Cs4[(UO2)2(GaOH)2(PO4)4]?H2O (UGaP1) and 
Cs[UO2Ga(PO4)2] (UGaP2) appear superficially similar, the reaction stoichiometries, 
durations, and perhaps most importantly pH are dramatically different.  For the 
preparation of both compounds, we noted a reduction in pH between the starting reaction 
mixtures and that of the final mother liquor.  The pH decreased from 9.1 to 7.1 during the 
 61 
crystallization of UGaP1 and from 2.4 to 1.9 during the formation of UGaP2.  The 
substitution of Cs2CO3 by CsCl in the preparation of UGaP2 plays a significant role in 
controlling the pH of these reactions.  The synthesis of UGaP1 and UGaP2 also proved 
to be highly sensitive to temperature, and changes by as little as 10 ?C had dramatic 
effects on yield, product crystallinity, and crystal size.  
Structure. Cs4[(UO2)2(GaOH)2(PO4)4]?H2O (UGaP1).  The structure of UGaP1 
was solved to reveal a three-dimensional framework of interconnected one-dimensional 
gallium phosphate and uranyl phosphate chains that run approximately perpendicular to 
one another.  The gallium phosphate chain (Figure 3.1) is composed of corner-sharing 
GaO6 octahedra and bridging PO4 tetrahedra that extend along the c axis, and can be 
formulated as 1? [Ga(OH)(PO4)2]4?.  We propose based on charge balance considerations 
and bond-valence sums that the Ga?O?Ga backbone that runs down the gallium 
phosphate chains is protonated.  The bond-valence sums for the O(21) and O(22) atoms 
in this chain are 1.12 and 1.16, which are values expected for hydroxyl sites.33,34  Not 
surprisingly, given the presence of cesium and uranium in this structure, the hydrogen 
atoms could not be reliably located.  This type of chain is similar to that found in the 
aluminophosphate mineral tancoite, LiNa2H[Al(PO4)2(OH)],35,36 and has been recognized 
in a large number of aluminum, gallium, and transition metal phosphates.14,37-43  The Ga?
O bond distances range from 1.940(7) to 2.036(7) ?.  The P?O bond distances show little 
variation and occur from 1.515(7) to 1.574(7) ?.  Selected bond distances and angles for 
UGaP1 are given in Table 3.4.  
 
 
 62 
 
 
 
 
 
 
 
 
 
 
Figure 3.1. A view of the one-dimensional 1? [Ga(OH)(PO4)2]4? chains composed of 
corner-sharing GaO6 octahedra and bridging PO4 tetrahedra that extend along the c axis 
in Cs4[(UO2)2(GaOH)2(PO4)4]?H2O (UGaP1).  50% probability ellipsoids are depicted.   
 63 
Table 3.4  Selected Bond Distances (?) and Angles (o) for Cs4[(UO2)2(GaOH)2(PO4)4] 
(UGaP1). 
Distances (?) 
U(1)?O(3)  2.364(7) Ga(2)?O(6) 1.984(7) 
U(1)?O(3)'  2.503(7) Ga(2)?O(10) 2.036(7) 
U(1)?O(4)  2.400(7) Ga(2)?O(15)  1.982(7) 
U(1)?O(5)  2.255(8) Ga(2)?O(21)  1.930(7) 
U(1)?O(7)  2.307(7) Ga(2)?O(22)  1.924(7) 
U(1)?O(17)  1.805(7) P(1)?O(1)  1.526(7) 
U(1)?O(18)  1.794(7) P(1)?O(2)  1.516(8) 
U(2)?O(9)  2.306(7) P(1)?O(3)  1.574(7) 
U(2)?O(11)  2.223(7) P(1)?O(4)  1.544(8) 
U(2)?O(13)  2.390(7) P(2)?O(5)  1.523(8) 
U(2)?O(14)  2.376(7) P(2)?O(6)  1.515(7) 
U(2)?O(14)  2.606(7) P(2)?O(7)  1.542(7) 
U(2)?O(19)  1.795(7) P(2)?O(8)  1.529(7) 
U(2)?O(20)  1.786(7) P(3)?O(9)  1.546(8) 
Ga(1)?O(2)  1.971(7) P(3)?O(10)  1.531(7) 
Ga(1)?O(8) 1.948(7) P(3)?O(11) 1.546(8) 
Ga(1)?O(12) 1.971(7) P(3)?O(12) 1.545(7) 
Ga(1)?O(16)  1.988(7) P(4)?O(13)  1.547(7) 
Ga(1)?O(21)  1.962(7) P(4)?O(14)  1.571(8) 
Ga(1)?O(22)  1.940(7) P(4)?O(15)  1.532(7) 
Ga(2)?O(1)  1.973(7) P(4)?O(16)  1.521(7) 
 64 
Angles (?) 
O(18)?U(1)?O(17)  178.3(3) O(20)?U(2)?O(19)  178.1(3) 
 
 65 
 There are two crystallographically unique uranium centers in UGaP1.  Both of 
these U atoms are found as part of uranyl, UO22+, cations with short U=O bond distances 
of 1.794(7) and 1.805(7) ? to U(1), and 1.786(7) and 1.795(7) ? to U(2).  In both cases 
the uranyl cations are nearly linear with O(18)?U(1)?O(17) and O(20)?U(2)?O(19) bond  
angles of 178.3(3)? and 178.1(3)?, respectively.  The phosphate anions bind the UO22+ 
cations to form UO7 pentagonal bipyramids with U(1)?O and U(2)?O distances being 
found from 2.255(8) to 2.503(7) ? and 2.223(7) to 2.606(7) ?, respectively.  These bond 
distances can be used to calculate bond-valence sums for the U(1) and U(2) centers of 
5.94 and 5.96, which are consistent with hexavalent uranium.33,34,44  The bond angles in 
the pentagonal plane show substantial variation because the phosphate anions are found 
in both chelating and bridging modes.  Therefore, there is an acute angle of 58.9(3)? in 
the equatorial plane ascribed to the chelation of the uranyl cation containing U(1) by a 
phosphate anion.  The remaining angles in this plane range from 63.1(3)? to 81.7(3)?.  
The same situation occurs for U(2) with an acute angle of 57.6(2)? and the other angles 
ranging from 61.9(3)? to 84.8(3)?.  The UO7 moieties edge-share to create dimers that are 
bridged by phosphate anions to create one-dimensional chains, shown in the Figure 3.2, 
that can be formulated as 1? [UO2(PO4)2]4?.  There are two different uranyl phosphate 
chains, one chain exclusively contains U(1) and the other U(2).  The one-dimensional 
topology of these chains is similar to that found in Sr[UO2(SeO3)2]?2H2O where one of 
the P?O bonds on each phosphate anion has been replaced by a stereochemically active 
lone-pair on Se(IV).45  These chains are distinct from those found in the one-dimensional 
uranyl phosphate, parsonite, Pb2[UO2(PO4)2].46 
 
 66 
 
 
 
 
 
 
 
 
Figure 3.2.  A depiction of the one-dimensional 1? [UO2(PO4)2]4? chains in 
Cs4[(UO2)2(GaOH)2(PO4)4]?H2O (UGaP1).  50% probability ellipsoids are depicted.  
 67 
The interconnection of the 1? [Ga(OH)(PO4)2]4? and 1? [UO2(PO4)2]4? substructures 
creates a three-dimensional 3? [(UO2)2(GaOH)2(PO4)4]4? anionic lattice that has 
intersecting channels running down the b and c axes. Small tunnels also extends down 
[111].  A view showing the largest channels, which measure approximately 3.5 x 7.3 ?, 
extending along b is shown in Figure 3.3.  There are four crystallographically unique Cs+ 
cations and a water molecule in UGaP1 that occupy these channels.  The Cs+ cations 
form between eight and ten long contacts with oxygen atoms in the structure with average 
distances of 3.254(8), 3.374(8), 3.171(8), and 3.243(8) ? to Cs(1), Cs(2), Cs(3), and 
Cs(4), respectively.  There is a short interaction of 2.869(13) ? between the water 
molecule and Cs(3).  In addition, the water molecule forms hydrogen-bonding 
interactions of 2.740(8) and 2.821(8) ? with phosphate oxygen atoms in the gallium 
phosphate chain.     
 Cs[UO2Ga(PO4)2] (UGaP2).  The structure of UGaP2 is three-dimensional, 
being constructed from one-dimensional 1? [Ga(PO4)2]3? gallium phosphate chains and 
one-dimensional uranyl phosphate chains, the former of which extend down the a axis.  
These gallium phosphate chains are formed from fused eight-membered rings of 
alternating corner-shared GaO4 and PO4 tetrahedra. (Figure 3.4) These types of rings are 
important building units in gallium phosphate chemistry and have been observed before 
in compounds such as [Ga(HPO4)(PO4)(OH)]?[(C2H7N)3N]?H2O6 and 
[NH3(CH2)4NH3][Ga(PO4)(HPO4)].47 The Ga atoms are the sites of ring fusion for these 
chains.  The Ga and P sites are easily distinguished from one another in these rings with 
average Ga?O and P?O bond distances of 1.814(5) and 1.532(5) ?, respectively.  The 
  
 68 
 
 
 
 
 
 
Figure 3.3.  An illustration of the three-dimensional 3? [(UO2)2(GaOH)2(PO4)4]4? anionic 
lattice of Cs4[(UO2)2(GaOH)2(PO4)4]?H2O (UGaP1) that has intersecting channels 
running down the b and c axes.  These channels house Cs+ cations and water molecules.  
Cs is shown in magenta, UO7 pentagonal bipyramids are shown in green, GaO6 octahedra 
in blue, and PO4 tetrahedra in yellow. 
 69 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 3.4.  A view of the one-dimensional 1? [Ga(PO4)2]3? gallium phosphate chains in 
Cs[UO2Ga(PO4)2] (UGaP2) formed from fused eight-membered rings of alternating 
corner-shared GaO4 and PO4 tetrahedra.  50% probability ellipsoids are depicted. 
 70 
two crystallographically unique PO43? anions each use two oxygen atoms to bridge 
between Ga centers.  The oxygen atoms that are not used in this fashion instead bind the 
uranium centers in the structure.  Selected bond distances and angles for UGaP2 can be 
found in Table 3. 5.  
 Unlike UGaP1 there is only one crystallographically unique U center in UGaP2 
that is found in the form of a UO7 pentagonal bipyramid.  There are two short U=O bonds 
of 1.774(5) and 1.779(5) ? that make up the approximately linear uranyl cation with an 
O?U?O angle of 177.2(2)?.  The equatorial U?O distances range from 2.283(5) to 
2.501(5) ? and are within normal limits.  Bond-valence sum calculations on U yield a 
value of 5.97, which is consistent with U(VI).33,34,44  The UO7 units edge-share to create 
dimers with a central inversion center.  These dimers are bridged by phosphate anions to 
create one-dimensional chains whose formula can be described as 1? [UO2(PO4)2]4?, and 
are illustrated in Figure 3.5  As can be seen from this figure, these chains are essentially 
the same as those found in UGaP1. 
 The gallium phosphate and uranyl phosphate chains run approximately 
perpendicular to one another to create a three-dimensional 3? [UO2Ga(PO4)2]1? framework 
with intersecting channels running down the a and b axes. (Figure 3.6)  These channels at 
their largest are 3.1 x 6.7 ?, and are of the size expected to house Cs+ cations in the 
absence of occluded water molecules.  The Cs+ cations form long ionic contacts with the 
surrounding anionic lattice with eight contacts ranging from 3.115(5) ? to 3.440(5) ?. 
 Thermal analysis. DSC data for UGaP1 demonstrate that the structure of the 
compound remains relatively stable at temperatures below 400 ?C. (Figure 3.7) The loss 
  
 71 
Table 3.5.  Selected Bond Distances (?) and Angles (o) for Cs[UO2Ga(PO4)2] (UGaP2). 
Distances (?) 
U(1)?O(1)  1.774(5) P(1)?O(3)  1.512(5) 
U(1)?O(2)  1.779(5) P(1)?O(4)  1.538(5) 
U(1)?O(3)  2.482(5) P(1)?O(5)  1.534(5) 
U(1)?O(4)  2.385(5) P(1)?O(6)  1.546(5) 
U(1)?O(4)'  2.501(5) P(2)?O(7)  1.552(5) 
U(1)?O(9)  2.283(5) P(2)?O(8)  1.552(5) 
U(1)?O(10)  2.295(5) P(2)?O(9)  1.505(5) 
Ga(1)?O(5)  1.807(5) P(2)?O(10)  1.519(5) 
Ga(1)?O(6)  1.824(5)   
Ga(1)?O(7)  1.801(5)   
Ga(1)?O(8)  1.822(5)   
Angles (?) 
O(1)?U(1)?O(2)  177.2(2)   
 
 
 
 
 
 
 
 
 
 72 
 
 
 
 
 
 
 
 
 
 
 
Figure 3.5  An illustration of the one-dimensional 1? [UO2(PO4)2]4? chains in 
Cs[UO2Ga(PO4)2] (UGaP2).  50% probability ellipsoids are depicted. 
 
 73 
 
 
 
 
 
 
 
Figure 3.6. A depiction of the three-dimensional 3? [UO2Ga(PO4)2]1? framework in 
Cs[UO2Ga(PO4)2] (UGaP2) with intersecting channels running down the a and b axes.  
Cs is shown in magenta, UO7 pentagonal bipyramids are shown in green, GaO4 tetrahedra 
in blue, and PO4 tetrahedra in yellow. 
 74 
 
 
-14
-12
-10
-8
-6
-4
-2
0
0 100 200 300 400 500 600
Temperature, 0C
H
e
a
t
 
f
l
o
w
,
 
 
m
W
.
.
150oC 172oC
536oC 546oC
 
 
 
 
 
 
 
Figure 3.7. DSC data of UGaP1 demonstrate relative stability of the structure at 
temperatures below 400 ?C. Two peaks at 150 ?C and 172 ?C correspond to loss of 
surface and interstitial water respectively.  
 75 
of surface and interstitial water occurs at 150 ?C and 172 ?C, respectively. Loss of 
hydroxyl groups and overall sluggish decomposition of the structure take place at 
temperatures above 400 ?C. The peaks cannot be assigned to defined events due to 
approach of the instrumentation limits.  
 The data for UGaP2 surprisingly exhibit a significant exothermic peak at 87 ?C, 
followed by a series of three successive endothermic peaks in the temperature range of 
127 ?C ? 155 ?C and single endothermic events at 260 ?C, 365 ?C, 508 ?C and 528 ?C. 
(Figure 3.8) The data clearly show that UGaP2 undergoes different structural 
rearrangements and phase transformations upon increases in temperature.  
 Ion-Exchange Studies. The exchange and mobility of interlayer cations in two-
dimensional uranyl compounds have been studied in great detail, particularly for layered 
uranyl phosphates.48  Both layered49 and open-framework uranyl vanadates, such as 
A(UO2)4(VO4)3 (A = Li, Na),28 have been shown to exhibit high cationic conductivities.  
We have also shown that the layered uranyl iodate, K[UO2(IO3)3], shows selective ion-
exchange of K+ for Cs+.50  Given the three-dimensional framework structures of UGaP1 
and UGaP2, we were interested in evaluating the potential exchange of Cs+ with H+, Na+, 
K+, Ca2+, Sr2+ and Ba2+ ions.  The concentrations of K+, Na+, Ca2+ and Ba2+ solutions 
were determined by potentiometric measurements using ion-selective electrodes.32,50  
This technique allows for the determination of both uptake and release of different ions 
by using different ion-selective electrodes.  Sr2+ and duplicated Ca2+ measurements were 
performed using atomic adsorption spectroscopy.  
 
 
 76 
 
 
 
-8
-7
-6
-5
-4
-3
-2
-1
0
0 100 200 300 400 500 600
Temperature, oC
H
e
a
t
 
f
l
o
w
,
 
m
W
.
 
.
87oC
127oC
147oC
155oC
260oC 365oC
508oC 528oC
555oC
 
 
 
 
 
 
Figure 3.8. DSC data of UGaP2. 
 77 
 Direct measurement of cation uptake often over- or underestimates actual ion-
exchange values owing to the typically large concentration of the exchanging ion in 
solution relative to the ion initially present in the material, as well as simple sorption by 
the material.  Therefore more realistic values can be obtained by measuring the 
concomitant release of Cs+ cations into solution.  For UGaP1 and UGaP2 no exchange 
of Cs+ was noted with H+, Na+, or K+.  However, the Cs+ cations in UGaP1 can be 
exchanged for Ca2+, Sr2+ and Ba2+ cations.  Direct Ca2+ uptake measured by ion-selective 
electrodes of 0.63(10) meq/g was found.  Cs+ cation release for this process yielded a 
similar value of 0.57(10) meq/g. These values are in perfect match with uptake, 0.61(10) 
meq/g, measured by atomic adsorption spectroscopy. Sr2+ ion-exchange capacity was 
determined as 0.40(7) meq/g. In the mixed 1:1 SrCl2/NaCl solutions again no Na+ uptake 
and reduced 0.35(5) meq/g Sr2+ uptake were detected. The smaller Sr2+ uptake value in 
the mixed solutions could be ascribed to the reduced concentration of Sr2+ and therefore 
increased volume to mass ratio during the exchange. When Cs+ cations are exchanged for 
Ba2+ cations a release value of 0.36(10) meq/g was found. The smaller channel size of 
UGaP2 apparently better accommodates Ca2+ than UGaP1 does, and a large uptake 
value of 1.79(30) meq/g was found; the Cs+ release was 1.06(20) meq/g. At the same 
time exchange of Cs+ with Sr2+ was not detected for UGaP2. UGaP1 and UGaP2 show 
similar ability to exchange Cs+ for Ba2+, and a release of 0.31(20) meq/g was measured 
for UGaP2. Crystallinity and absence of structural change in the both UGaP1 and 
UGaP2 sample were monitored by powder diffraction analysis of all samples before and 
after ion-exchange.   
 
 78 
CONCLUSIONS 
 In this work we have demonstrated that uranyl gallium phosphates can be 
prepared under mild hydrothermal conditions.  Our original goal was to prepare three-
dimensional framework compounds by incorporating octahedral GaO6 building units.  
The crystal structure of Cs4[(UO2)2(GaOH)2(PO4)4]?H2O (UGaP1) indicates that this 
strategy was successful.  However, the structure of Cs[UO2Ga(PO4)2] (UGaP2), which 
contains tetrahedral GaO4 units, demonstrates that octahedral gallium is not necessary for 
the construction of open-framework uranyl gallium phosphates.  
 Thermal analysis revealed the absence of any structural of UGaP1 up to 400 ?C. 
Ion-exchange experiments show that the Cs+ cations in UGaP1 can be highly selectively 
exchanged with Sr2+ with the uptake of 0.4 meq/g in the presence of Na+ cations. 
Summarizing these data we can recommend UGaP1, as a potential 90Sr selective 
material, which should be studied further under conditions more closely approximating 
those present in nuclear waste.  
 
 
 
 
 
 
 
 
 
 79 
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15. Chippindale, A. M. Chem. Mater. 2000, 12, 227. 
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22. Sykora, R. E.; Albrecht-Schmitt, T. E. Inorg. Chem. 2003, 42, 2179. 
23. Sullens, T. A.; Jensen, R. A.; Shvareva, T. Y.; Albrecht-Schmitt, T. E. J. Am. Chem. 
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24. a) Burns, P. C.; Miller, M. L.; Ewing, R. C. Can. Mineral. 1996, 34, 845.  b) Burns, 
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178, 499. 
 
83 
CHAPTER 4 
SYNTHESIS, STRUCTURES, AND PROPERTIES OF THE 
MULTIFUNCTIONAL URANYL VANADIUM PHOSPHATE FRAMEWORKS  
 
ABSTRACT 
Two novel framework uranyl vanadium phosphate materials were synthesized 
under hydrothermal conditions.  Similar reactions of UO2(NO3)2?6H2O, V metal, H3PO4 
and various alkaline metal chlorides CsCl, KCl, or RbCl yielded different types of 
structures. Three-dimensional Cs2[UO2(VO2)2(PO4)2]?nH2O (UVVP) is constructed from 
uranyl phosphate chains, that are joined together by chains of corner-sharing VO5 
distorted square pyramids. Channels along the b and c axes are filled with Cs+ cations. 
Alignment of terminal V=O bonds in all VO5 units along the c axis creates the overall 
polarity of the structure. Due to the polar structure, UVVP exhibits non-linear optical 
properties.  Isostructural K4(UO2)(VO)4(OH)2(PO4)4 (KUVIVP) and 
Rb4(UO2)(VO)4(OH)2(PO4)4  (RbUVIVP) contain VIV in an octahedral coordination 
environment.  Their frameworks are constructed from vanadyl phosphate layers, 
interconnected by uranyl tetragonal bipyramids.  There are channels, filled with K+ or 
Rb+, in all three perpendicular directions.  Antiferromagnetic ordering at 52 K and Cs+- 
selective ion-exchange properties were found and characterized.  
 
 84 
INTRODUCTION 
 Rich and diverse crystal chemistry of the vanadium compounds arises from the 
ability of trivalent, tetravalent and pentavalent vanadium to adopt a wide range of 
coordination environments, from tetrahedral through trigonal bipyramidal and square 
pyramidal to octahedral.1 For instance, the family of vanadium phosphates, most 
recognized for their magnetic and catalytic properties,2,3 is composed of more than 130 
members with one, two or three-dimensional crystal structures.2-5 To a certain degree, this 
structural flexibility is replicated in the class of uranyl-containing vanadium compounds.  
In the layered compounds with the structure of mineral carnotite of the general formula 
M2(UO2)2V2O8 nH2O,6-8 (M = K, Na, Ag, etc.) the centrosymmetric V2O86- groups are 
formed from two edge-shared VO5 square pyramids with terminal oxygen atoms pointed 
in opposite directions.  Three-dimensional A(UO2)2(VO4)3  compounds, (A = Li and 
Na),9 that have the cation conductivity properties, comparable with NaSiCON and 
LiSiCON materials, as well as Pb(UO2)(V2O7),10 also crystallized in the centrosymmetric 
space groups I41/mad and P21/n respectively, and contain vanadium tetrahedra in the 
structure.  On the other hand, the structure of K2[(UO2)2(VO)2(IO6)2O] H2O,11 composed 
completely of only distorted octahedra, including distorted VO6, is polar and crystallized 
in the Pba2 space group.  Due to the polarity of the structure this material demonstrates 
non-linear optical properties.  
 In all described uranyl-containing vanadium materials, either with layered or 
three-dimensional structures, vanadium is present in the +5 oxidation state.  Numerous 
vanadium phosphates, that incorporate only tetravalent vanadium, or mixed valent 
VIV/VV units, such as 
-LiVIVOPO4,12 Zn2(VIVO)(PO4)2,13 Ba3VIV/VVO3(PO4)3,14 
 
 85 
Na5(VIVO)2(PO4)3 H2O,15 and many others2 demonstrate paramagnetic behavior in the 
range of temperatures between 50 and 300 K, due to the presence of d1 unpaired electron 
on the vanadium center, and antiferromagnetic or ferromagnetic ordering at temperatures 
5-40 K as a consequence of different super-exchange mechanisms of the various types of 
V-P-O chains present in the structures.  
 In this chapter we describe the structure of two novel framework uranyl vanadium 
phosphates: Cs2[UO2(VO2)2(PO4)2]?nH2O (UVVP) and isostructural 
K4(UO2)(VO)4(OH)2(PO4)4 (KUVIVP) and Rb4(UO2)(VO)4(OH)2(PO4)4 (RbUVIVP), 
along with their physical properties: the thermal behavior, second harmonic generation 
(SHG) of laser light of UVVP, selective ion-exchange properties and magnetic properties 
for KUVIVP and  RbUVIVP.  
 
EXPERIMENTAL 
Syntheses.  UO2(NO3)2?6H2O (98%, Alfa-Aesar), V powder (99.99%, Sigma 
Aldrich), H3PO4 (98%, Aldrich), KCl (99.997%, Alfa-Aesar), RbCl (99.975%, Alfa-
Aesar), and CsCl (99.9%, Cerac) were used as received. V powder stored in the glove 
box was loaded in argon atmosphere. The reactions were run in PTFE-lined Parr 4749 
reaction vessels.  Distilled and Millipore filtered water with a resistance of 18.2 MW?cm 
was used in all experiments.  
 Cs2[UO2(VO2)2(PO4)2]?nH2O (UVVP). UO2(NO3)2?6H2O  (0.289 g, 0.576  
mmol), H3PO4 (0.169 g, 1.72 mmol), CsCl (0.484 g, 2.88 mmol), and 1 mL of Millipore-
filtered water were mixed in the 23 mL autoclave, followed by addition of V metal 
powder (0.080 g, 1.16 mmol), separately weighed in the glove box.  The reaction was run 
 
 86 
in sealed autoclave at 190 ?C in a box furnace for 5 days and then cooled at a rate of 9 
?C/hour to room temperature.  Clusters of large bright yellow crystals of UVVP, reaching 
several mm in length, were isolated, washed with methanol, and allowed to dry. Yield, 
515 mg (98% yield based on U).   
K4(UO2)(VO)4(OH)2(PO4)4 (KUVIVP). UO2(NO3)2?6H2O  (0.395 g, 0.787 
mmol),  H3PO4 (0.231 g, 2.36 mmol), KCl (0.293 g, 3.94 mmol) and V (0.080 g, 1.6 
mmol) were mixed in 23 mL PTFE-lined autoclave with 1 mL of water. Then reaction 
was heated at 190 ?C for five days and cooled to room temperature at a rate of 9 ?C/hour. 
After decantation of the mother liquid the only solid product of the reaction - bright blue 
prismatic crystals of KUVIVP were revealed. The yield of KUVIVP was 0.340 g (40.5 % 
yield based on the U).   
Rb4(UO2)(VO)4(OH)2(PO4)4 (RbUVIVP). UO2(NO3)2?6H2O  (0.334 g, 0.665 
mmol),  H3PO4 (0.196 g, 1.99 mmol), RbCl (0.402 g, 3.33 mmol) and V (0.068 g, 1.3 
mmol) were mixed in 23 mL PTFE-lined autoclave followed by addition of 1 mL of 
water. After heating at 190 ?C for five days and cooling at a 9 ?C/hour to room 
temperature, the reaction vessel was opened and the product mixture, containing blue 
prism crystals of RbUVIVP and yellow powder product, was washed with methanol and 
dried at the air. The yield of RbUVIVP was 0.426 mg (50.9 % yield based on the U).   
Crystallographic Studies.  Crystals of UVVP, KUVIVP, and RbUVIVP were 
mounted on glass fibers and aligned on a Bruker SMART APEX CCD X-ray 
diffractometer.  Intensity measurements were performed using graphite monochromated 
Mo Ka radiation from a sealed tube and monocapillary collimator.  SMART (v 5.624) 
was used for preliminary determination of the cell constants and data collection control.  
 
 87 
The intensities of reflections of a sphere were collected by a combination of 3 sets of 
exposures (frames).  Each set had a different f angle for the crystal and each exposure 
covered a range of 0.3? in w.  A total of 1800 frames were collected with an exposure 
time per frame of 30 s for the crystals of UVVP, KUVIVP, and RbUVIVP.  
 Determination of integrated intensities and global refinement were performed 
with the Bruker SAINT (v 6.02) software package using a narrow-frame integration 
algorithm.  A face-indexed analytical absorption correction was initially applied using 
XPREP, where individual shells of unmerged data were corrected analytically.16  These 
files were subsequently treated with a semiempirical absorption correction by 
SADABS.17  The program suite SHELXTL (v 6.12) was used for space group 
determination (XPREP), direct methods structure solution (XS), and least-squares 
refinement (XL).16  The final refinements included anisotropic displacement parameters 
for all atoms.  Secondary extinction was not noted for the crystals of UVVP, KUVIVP, 
and RbUVIVP.  Some crystallographic details are given in Table 4.1.  Atomic 
coordinates, symmetry information, displacement parameters, and occupancy for all 
atoms can be found in the Tables 4.2, 4.3, and 4.4 for UVVP, KUVIVP, and RbUVIVP 
respectively.   
 Thermal analysis.  The data were collected using differential scanning 
calorimeter TA Instrument, model 2920.  The samples of known mass encapsulated in an 
aluminum container, were heated under nitrogen atmosphere from 30 ?C to 600 ?C with a 
heating rate of 10 ?C /minute.  
Non-linear optical properties. SHG was investigated using 1064 nm excitation 
laser pulses from a Q-switched Nd:YAG laser (Continuum Surelite I-10). A 
 
 88 
Table 4.1.  Crystallographic Data for Cs2[UO2(VO2)2(PO4)2]?nH2O (UVVP), 
K4(UO2)(VO)4(OH)2(PO4)4 (KUVIVP) and Rb4(UO2)(VO)4(OH)2(PO4)4 (RbUVIVP) 
Compound UVVP KUVIVP  RbUVIVP 
Formula Mass 901.99 1106.07 1243.26 
Color and habit yellow prism blue plate blue plate 
Crystal System orthorhombic orthorhombic Orthorhombic 
Space group Cmc21(No. 36) Immm (No.71 ) Immm (No.71 ) 
a (?) 20.7116(14) 7.3803(7) 7.4370(7) 
b (?) 6.8564(5) 9.1577(8) 9.1662(8) 
c (?) 10.5497(7) 17.0898(16) 17.2415(15) 
V (?3) 1498.13(18) 1155.04(18) 1175.34(18) 
Z 4 2 2 
T (K) 193 193 193 
l (?) 0.71073 0.71073 0.71073 
Maximum 2q (deg.)  56.62 56.58 56.74 
rcalcd (g cm?3) 3.999 3.180 3.513 
m(Mo Ka) (cm?1) 170.76 96.48 158.39 
R(F) for Fo2 > s(Fo2) a 0.0265 0.0533 0.0551 
Rw(Fo2) b 0.0602 0.1407 0.1461 
a ( )R F F F F= -
 

o c o .  
b ( ) ( )R F w F F wF
w o
2
o
2
c
2 2
o
4
1 2
= - 
 
  . 
 
 
 
 
 
 
 89 
Table 4.2.  Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 
Cs2[UO2(VO2)2(PO4)2]?nH2O (UVVP) 
Atom Symmetrya x y z Ueq (?2) b Occup. 
U(1) 4  a  m 0 0.0326(5) -0.02493(4) 0.01259(10) 1 
V(1) 8  b  1 -0.25770(5) -0.2961(16) 0.18303(13) 0.0134(3) 1 
P(1) 8  b  1 -0.12106(9) -0.0815(3) 0.2254(2) 0.0132(4) 1 
O(1) 8  b  1 -0.0809(3) -0.1215(9) 0.3441(5) 0.0215(12) 1 
O(2) 8  b  1 -0.1609(2) 0.1081(8) 0.2442(6) 0.0207(11) 1 
O(3) 8  b  1 -0.0767(3) -0.0678(9) 0.1113(6) 0.0241(13) 1 
O(4) 8  b  1 -0.1657(2) -0.2593(8) 0.2052(5) 0.0160(10) 1 
O(5) 8  b  1 -0.2709(3) -0.0641(7) 0.2323(6) 0.0195(13) 1 
O(6) 8  b  1 -0.2648(3) -0.2942(9) 0.0320(6) 0.0232(13) 1 
O(7) 4  a  m 0 -0.2040(12) -0.0944(7) 0.0196(16) 1 
O(8) 4  a  m 0 0.2726(11) -0.9540(9) 0.0184(16) 1 
O(9) 4  a  m 0 0.544(3) 0.241(3) 0.068(11) 0.59(5) 
Cs(1) 8  b  1 -0.12432(2) -0.46363(7) -0.05798(4) 0.02101(15) 1 
a Symmetry describes multiplicity, Wyckoff parameter and symmetry of the atomic site. 
b Ueq is defined as one-third of the trace of the orthogonalized Uij tensor. 
 
 90 
Table 4.3.  Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 
K4(UO2)(VO)4(OH)2(PO4)4 (KUVIVP) 
Atom Symmetrya x y z Ueq (?2) b Occup. 
U(1) 2  a  mmm ? ? ? 0.0078(3) 1 
V(1) 8  m  m 0.7058(3) ? 0.76487(11) 0.0092(4) 1 
P(1) 8  l  m ? 0.7579(3) 0.66892(17) 0.0081(6) 1 
O(1) 4  e  2mm 0.7435(18) ? ? 0.016(2) 1 
O(2) 8  l  m ? 0.6805(10) 0.5902(5) 0.0166(18) 1 
O(3) 8  l  m ? 0.6429(10) 0.7368(5) 0.0123(17) 1 
O(4) 16  o  1 0.6721(9) 0.8479(7) 0.6743(4) 0.0155(13) 1 
O(5) 8  m  m 0.8080(13) ? 0.6825(5) 0.0175(19) 1 
O(6) 4  i  mm2 ? ? 0.8660(9) 0.023(3) 1 
K(1) 8  l  m 0 0.3052(8) 0.4122(3) 0.048(2) 0.751(18) 
K(2) 2  d  mmm ? 0 ? 0.114(9) 1 
a Symmetry describes multiplicity, Wyckoff parameter and symmetry of the atomic site. 
b Ueq is defined as one-third of the trace of the orthogonalized Uij tensor. 
 
 
 
 
 
 
 
 
 
 
 91 
Table 4.4.  Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 
Rb4(UO2)(VO)4(OH)2(PO4)4 (RbUVIVP) 
Atom Symmetrya x y z Ueq (?2) b Occup. 
U(1) 2  a  mmm ? ? ? 0.0072(3) 1 
V(1) 8  m  m 0.7052(3) ? 0.76599(12) 0.0083(5) 1 
P(1) 8  l  m ? 0.7571(3) 0.66934(17) 0.0082(6) 1 
O(1) 4  e  2mm 0.7397(19) ? ? 0.015(3) 1 
O(2) 8  l  m ? 0.6779(11) 0.5910(5) 0.0145(19) 1 
O(3) 8  l  m ? 0.6432(10) 0.7367(5) 0.0108(18) 1 
O(4) 16  o  1 0.6711(9) 0.8473(7) 0.6742(4) 0.0128(13) 1 
O(5) 8  m  m 0.8047(13) ? 0.6842(6) 0.017(2) 1 
O(6) 4  I  mm2 ? ? 0.8644(9) 0.023(3) 1 
Rb(1) 8  l  m 0 0.3083(4) 0.41202(15) 0.0313(10) 0.608(8) 
Rb(2) 2  d  mmm ? 0 ? 0.0724(16) 1 
a Symmetry describes multiplicity, Wyckoff parameter and symmetry of the atomic site. 
b Ueq is defined as one-third of the trace of the orthogonalized Uij tensor. 
 
 
 
 
 
 
 
 
 
 
 92 
Scientech volume absorbing calorimeter was used to measure average laser power.  SHG 
at 532 nm was visually observed in a darkened room from a polycrystalline sample of 
UVVP contained in a glass tube and was quantified using a band-pass optical filter, IR 
insensitive photomultiplier (1P28), and a signal averaging digital storage oscilloscope 
(Tektronix TDS 640A), as the intensity of the unfocused laser beam was increased above 
the SHG threshold. At a beam cross section averaged intensity of 3.6 MW/cm2, the SHG 
intensity from UVVP was 1500 times weaker that the signal observed from a commercial 
rare-earth-based ceramic frequency upconverting laser beam finder (Kentek View-It). 
Magnetic properties.  Magnetic susceptibility measurements were conducted 
using a Quantum Design superconducting interference device (SQUID), under applied 
fields ranging from 100 to 10000 gauss as a function of temperature over the range of 5 ? 
320 K and magnetization data were collected at 5K in fields ranging from 0 ? 10,000 
gauss.  Samples were doubly encapsulated in aluminum containers, which contributed 
significantly to the measured signal, especially at higher temperatures and for samples 
with a low inherent susceptibility.  Empty containers were run independently under the 
same conditions and the data used directly for background subtraction.  Diamagnetic 
contributions to the data were also calculated and used to correct the measured 
susceptibility. 
 The temperature dependent magnetic susceptibility data were analyzed assuming 
Curie-Weiss behavior with an added temperature independent term, c = C / (T-q) + cTIP, 
where C and q are Curie and Weiss constants and cTIP is the temperature-independent 
contribution to the susceptibility.  C is related to the effective magnetic moment 
 
 93 
2/1
2
0
3
	




=
B
eff N
kC
mm in which N0 is Avogadro?s number and mB is the Bohr magneton 
(0.927 x 10-20 erg/Gauss).  For cases in which cTIP is small, the effective magnetic 
moment can be obtained directly from the slope of the temperature dependence versus 
inverse magnetic susceptibility. 
Ion-Exchange Studies.  NaCl, KCl, CsCl, CaCl2 and SrCl2 solutions with 
concentrations of 1?10-3 M and 1?10-2 M were used in order to estimate ion-exchange 
capacities of all materials.  Ion-exchange properties, in actual fact, concentrations of the 
solutions of different cations were measured with two different methods: classic 
potentiometric method with ion-selective electrodes for K+, Na+ and  Cs+ uptake,18 using 
Accumet A15 pH meter, and atomic adsorption spectroscopy, using Varian 240 AA 
spectrometer with hollow cathode Ca and Sr lamps for Ca2+ and Sr2+ uptake.   
Ion-selective electrodes were made in accordance with Fluka-recommended 
compositions and silver/silver chloride electrode as a reference.18 In order to prevent 
contamination of tested solutions with KCl the reference electrode with double junction 
and lithium acetate as a bridging electrolyte were utilized.  
In all cases samples were equilibrated in capped 5 mL vials with different cation 
solutions of known concentration for 48 hours at constant shaking, and then the change in 
the concentrations was determined.  
The approximate volume to mass ratio 200:1 (4 mL of the solution for 0.02 g of 
sample) was used in all experiments. 
 
 
 
 94 
RESULTS AND DISCUSSION 
 Syntheses.  The utilization of the same reaction with only varied alkali metal 
chloride, CsCl - in the case of UVVP, KCl - KUVIVP, and RbCl -  RbUVIVP,  reveals the 
products, distinct not only in oxidation state and coordination number of vanadium, but 
also in the construction pattern of the structures.  All our attempts to synthesize the 
identical to UVVP structure with K+ and Rb+ charge-balancing cations, as well as 
KUVIVP and RbUVIVP in the Cs-form, or even in the mixed-cations form failed. But at 
the same time KUVIVP and RbUVIVP did not undergo any structural changes after 
substitution of K+ or Rb+ with Cs+ by ion-exchange. We expect that the reason for this 
phenomena can be found in the thermodynamics of the synthetic reactions. In situ 
scanning microcalorimetry with slowly increasing temperature may be useful in order to 
solve this discrepancy, because it will give a possibility to observe all heat effects that 
correspond to all stages of synthesis of both UVVP and K(Rb)UVIVP.  Running of 
multiple identical reactions also helps to identify every intermediate product of the 
reactions at different temperatures and make conclusions about driving forces and 
limitations and thus about major thermodynamic factors for both reactions.19-21 
 Vanadium metal powder was used as a source of vanadium. This synthetic 
method was previously studied with Ti and V, and in both cases yielded mixed-valent 
TiIII/TiIV and VIII/VIV compounds.22,23 We suggest that for oxidation of V0/VIII, protons 
from the phosphoric acid serve as oxidizer with subsequent release of hydrogen gas. In 
further oxidation of VIII to VIV and VV oxygen from air, present in the reaction vessel, or 
dissolved in water, can possible be involved.  
 
 95 
 Structures. Cs2[UO2(VO2)2(PO4)2]?nH2O (UVVP). The structure of UVVP 
consists of uranyl cations bound by phosphate to yield UO6 tetragonal bipyramids.  These 
units are bridged by phosphate to yield one-dimensional chains that run down the c axis.  
This basic one-dimensional topology is recognized to occur in several uranyl phases 
 including Cu2[UO2(PO4)2].24  The uranyl phosphate chains are in turn linked by chains of 
corner-sharing VO5 distorted square pyramids that run down the b axis into a novel open-
framework structure that has intersecting channels that occur along the b and c axes as is 
shown in Figure 4.1.  The channels running down the b axis are approximately 5.5 ? x 
10.9 ?, whereas those running down the c axis are 5.0 x 9.5 ?.  These channels are 
occupied by Cs+ cations and water molecules.  One the most apparent features of this 
structure is that the VO5 units are aligned so that the single terminal oxo atoms of these 
polyhedra are all aligned along the c axis as is shown in Figure 4.1.  
Cs2[UO2(VO2)2(PO4)2]?nH2O crystallizes in polar orthorhombic space group Cmc21.  As 
such, c is the polar axis, and the origin of this polarity lies in the alignment of the vanadyl 
units.  The alignment of the vanadyl units is reminiscent of the alignment of titanyl units 
in the key NLO material KTiOPO4 (KTP).25, 26         
 The selected U-O, V-O and P-O bond distances, and angles are shown in Table 
4.5.  The UO6 units in Cs2[UO2(VO2)2(PO4)2]?nH2O display two short U=O bond 
distances of 1.772(7) and 1.781(8) ?, that define the uranyl cation.  These bond distances 
are within the typical range for U=O distances. Longer U?O bonds to the equatorial 
oxygen atoms from the phosphate anions range from 2.250(6) to 2.256(5) ?.  These 
distances were used to calculate a bond-valence sum for the U center of 6.32, which is 
consistent with U(VI).28   
 
 96 
 
Figure 4.1.  Depiction of the channels of UVVP, extended along b and c axes, occupied 
by Cs+ cations.  Green ? uranium, blue ? vanadium, yellow ? phosphorus, purple ? 
cesium centers.  
 
 97 
Table 4.5. Selected Bond Distances (?) and Angles (?) for Cs2[UO2(VO2)2(PO4)2]?nH2O 
(UVVP) 
Distances (?) 
U(1)-O(8)  1.772(7) V(1)-O(4) 1.936(5) 
U(1)-O(7) 1.781(8) V(1)-O(5?) 1.999(5) 
U(1)-O(3) 2.250(6) P(1)-O(3) 1.518(6) 
U(1)-O(1) 2.256(5) P(1)-O(1) 1.527(5) 
V(1)-O(6) 1.600(6) P(1)-O(4) 1.545(5) 
V(1)-O(5) 1.696(5) P(2)-O(2) 1.552(6) 
V(1)-O(2) 1.921(5)   
Angles (?) 
O(8)?U(1)?O(7)  177.5(4) O(5)?V(1)?O(2) 94.4(3) 
O(5)?V(1)?O(6) 106.4(3) O(5)?V(1)?O(4) 89.9(2) 
 
 
 
 
 
 
 
 
 
 
 
 98 
 The VO5 units contain VO2+ vanadyl cations with two short V=O bonds of 
1.600(6) and 1.696(5) ?.  The shorter of these bonds is to the terminal oxo atom.  The 
remaining three V?O bonds range from 1.921(5) to 1.999(5) ?, yielding a bond-valence 
sum for the V atom of 5.08.28, 29  The tetrahedral phosphate anion shows typical P?O 
distances ranging from 1.518(6) to 1.552(6) ?.  Finally, charge balance for the anionic 
lattice formed by the UO6, VO5, and PO4 units is maintained by the Cs+ cations that form 
contacts with surrounding oxygen atoms that occur from 3.105(6) to 3.395(6) ?.  There 
are also partially occupied water molecules within smaller channels in the structure.  
There are 0.59 water molecules per formula unit.  The fundamental building unit in 
UVVP is shown in Figure 4.2. 
 K4(UO2)(VO)4(OH)2(PO4)4 (KUVIVP) and Rb4(UO2)(VO)4(OH)2(PO4)4 
(RbUVIVP).  KUVIVP and RbUVIVP have similar framework structures based on the 
interconnection of vanadyl phosphate layers by uranyl tetragonal bipyramids. The 
fundamental building unit of KUVIVP and RbUVIVP is shown in Figure 4.3. Selected 
bond distances and angles are given in the Table 4.6.  The vanadyl phosphate layer 
includes one crystallographically unique vanadium atom connected to six oxygen atoms. 
This connection leads to the formation of distorted coordination octahedra with one short 
vanadyl V?O(5) distance 1.598(9) ? (1.592(10) ?), one long V ? O6 bond - 2.301(11) ? 
(2.282(12) ?) in trans position to vanadyl, and four equatorial bonds with lengths ranging 
from 1.958(6) ? to 2.061(6) ? (from 1.966(7) ? to 2.075(6) ?). Distances and angles 
given in parenthesis represent the data for RbUVIVP.The bond valency sum calculated 
from these distances confirms vanadium +4 oxidation state.28 Close packing of two 
   
 
 99 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 4.2.  The fundamental building unit of UVVP shown in 50% probability thermal 
ellipsoids. 
 
 100 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 4.3.  Thermal ellipsoid plot of the fundamental unit of K4(UO2)(VO)4(OH)2(PO4)4 
(KUVIVP) and Rb4(UO2)(VO)4(OH)2(PO4)4 (RbUVIVP) at 50% probability.   
 
 101 
Table 4.6. Selected Bond Distances (?) and Angles (?) for K4(UO2)(VO)4(OH)2(PO4)4 
(KUVIVP). Data for  Rb4(UO2)(VO)4(OH)2(PO4)4 (RbUVIVP) are given in parathensis.   
Distances (?) 
U(1)-O(1)  1.797(13) (1.783(14)) V(1)-O(6) 2.301(11) (2.282(12)) 
U(1)-O(2) 2.261(9)   (2.262(9)) V(1)-V(1) 3.038(4)   (3.053(4)) 
V(1)-O(5) 1.598(9)   (1.592(10)) P(1)-O(4) 1.517(6)   (1.520(7)) 
V(1)-O(4) 1.958(6)   (1.966(7)) P(1)-O(2) 1.520(9)   (1.534(10)) 
V(1)-O(3) 2.061(6)   (2.075(6)) P(2)-O(3) 1.567(9)   (1.562(9)) 
Angles (?) 
O(8)?U(1)?O(7)  180.00(1) (180.00(2)) O(4)?V(1)?O(3) 90.6(3)     (91.2(3)) 
O(5)?V(1)?O(6) 166.9(4)   (165.7(5)) V(1)?O(6)?V(1) 82.6(5)     (83.9(5)) 
 
 
 
 
 
 
 
 
 
 
 
 
 
 102 
vanadium centers with V-V distance 3.038(4) ?(3.053(4) ?) results in the formation of 
face-shared V2O9 dimers where two equatorial O(4) and axial O(6) atoms belong to both 
coordination polyhedra.(Figure 4.4) These dimers were previously described in the 
literature, and for the first time were reported as a part of the (VO)2H4P2O9 structure.30,31 
(VO)2H4P2O9 is a key precursor for the synthesis of vanadyl pyrophosphate (VO)2P2O7, 
which is a well known technologically important catalyst in the oxidation of butane to the 
maleic anhydride3,32 that has been studied in detail.   
 Six equatorial oxygen atoms of the V2O9 building units are bridged to the six 
other vanadium dimers through phosphate groups, while two vanadyl O(5) and one 
opposite axial O(6) atoms remain terminal. There is an undefined electron density area 
located at the distance 1.55(2) ? from O(6). We speculate that the density could be 
assigned to one more, highly disordered H2PO4 phosphate group, but there is not enough 
structural information to prove this suggestion.  
 Each PO4 group is tetrahedral with three typical P-O bonds 1.517(6) ? - 1.520(9) 
? (1.520(7) ? - 1.534(10) ?) and one longer 1.567(9) ? (1.562(9) ?) bond, which 
corresponds to the 3-oxo bridge. The interaction of V2O9 and PO4 units create the layer in 
the [ab] plane, as is shown in the Figure 4.4. The vanadium phosphate layers with similar 
topology are found in the structures of (NH4)Zn(H2O)(VO)2(PO4)2(H2PO4)33 and 
MZn(H2O)(VO)2(PO4)2(H2PO4) (M = K+, Rb+, and Cs+).34  It is important to note that 
highly disordered phosphate groups in these structures are also found at the same location 
relative to the vanadium phosphate layer, as undefined electron density in KUVIVP and 
RbUVIVP. The layers are joined together by uranyl tetragonal bipyramids. There is one 
  
 
 103 
 
 
  
Figure 4.4.  Depiction of essential building blocks of the structures of KUVIVP and 
RbUVIVP.  V2O9 dimer, constructed from two vanadium octahedra, sharing two 
equatorial and one axial oxygen atoms (top) and vanadyl phosphate layer (bottom). 
Cations (purple) occupy the channels 2.8 ? ? 4.4 ? along c axis. Blue - vanadium 
polyhedra, yellow ? phosphate groups.  
 
 104 
crystallographically unique uranium center in the structure that belongs to linear UO22+  
cation and indeed has two axial uranyl oxygen atoms with a distance of 1.797(13) ? 
(1.783(14) ?) and an angle of 180.000(1)? (180.000(2)?). Four equatorial oxygen bonds 
with lengths 2.261(9) ? (2.262(9) ?) are bridged to phosphate groups of vanadium 
phosphate layer creating a negatively charged framework of [(UO2)(VO)4(OH)2(PO4)4]4- 
with a system of channels, parallel to the a, b, and c axes, filled with K+ (Rb+) cations. 
The channels along the a and b axes are shown in the Figures 4.5 and 4.6 respectively.  
There are two crystallographically distinct cationic sites in this structure. One is fully 
occupied with an alkali metal cation, either K+, or Rb+, coordinated to 12 oxygen atoms 
with coordination distances ranging from 3.163(8) ? to 3.308(9) ? (3.343(10) ? - 
3.550(7) ?). The other cation is in an 8-coordinate environment. It is disordered and only 
partially occupied with 0.751(18) of K+ and 0.608(8) of Rb+, in the unit cell. This partial 
occupancy creates the small positive charge defficiency, that can be neutralized by 
protonation of terminal oxygen atoms of the framework and again, could be ascribed to 
the presence of an additional disordered phosphate group in the structure. Finally, the 
formula of the compound is proposed as ideal M4[(UO2)(VO)4(OH)2(PO4)4], that does not 
reflect the partial occupancy of the cationic sites.  
Thermal analysis. We have studied the thermal behavior of UVVP and KUVIVP 
as potential Cs+ and Sr2+ selective ion-exchange materials, in order to test their ability to 
preserve the structure at high-temperature conditions of actual nuclear waste.  
DSC data for the UVVP reveal two significant endothermic events upon an 
increase in temperature to 600 ?C. (Figure 4.7) The first peak occurs at 150 ?C, which can  
  
 
 105 
 
 
 
 
 
 
 
 
Figure 4.5.  Depiction of the channels in the framework of KUVIVP and RbUVIVP, 
filled with K+ or Rb+ cations, extended along the a axis. Blue- vanadium, yellow ? 
phosphorus, green ? uranium centers, purple ? K+ or Rb+ cations.  
 
 106 
 
 
 
 
 
 
 
 
 
 
Figure 4.6.  A view of the framework of KUVIVP and RbUVIVP along the b axis.  
 
 
 107 
 
 
 
-2
-1.8
-1.6
-1.4
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
30 130 230 330 430 530
Temperature, oC
H
e
a
t
 
f
l
o
w
,
 
m
W
.
 
.
150oC
570oC
510oC
 
 
 
 
 
 
Figure 4.7.  DSC data for UVVP demonstrate thermal stability up to 510 ?C. 
 
 108 
be assigned to the removal of the surface and interstitial 0.59 water molecules.  The 
second event, composed of two peaks, the smaller at 510 ?C and the larger ? at 550 ?C, 
corresponds to the decomposition of material. We can suggest that the structure of UVVP 
remains stable and maintains crystallinity at the temperatures under 500 ?C. 
 The data for KUVIVP demonstrate the loss of water content at 160 ?C, and a series 
of sequential reconstructions of the framework at 310 ?C, 330 ?C, 510 ?C and 550 ?C. 
(Figure 4.8) Amorphization of the structure after heating to 600 ?C is confirmed by 
powder diffraction.  
 Non-linear optical properties. One of the consequences of the polarity in the 
structure of UVVP is that the compound should exhibit the SHG of laser light; that is, it 
should act as a NLO material.  SHG was investigated using 1064 nm excitation laser 
pulses from a Q-switched Nd:YAG laser. SHG at 532 nm was observed from a 
polycrystalline sample of UVVP. The response is substantially weaker than that of a 
commercial ceramic frequency doubling laser beam finder (Kentek View-It). At the same 
time the sample of  UVVP  shows a 70 times larger response than -quartz. Thus, 
observed non-linear optical properties can confirm the polar nature of the structure, but 
UVVP cannot be considered as an effective NLO material.  
 Magnetic properties. Magnetization of UVVP varies linearly with magnetic field, 
as is shown in Figure 4.9. The temperature dependence of the magnetic susceptibility of 
UVVP, measured in a constant field of 10000 G, is shown in Figure 4.10.  The magnetic 
signal at high temperatures is almost equal to the background, consistent with the 
expectation that V in this compound is present as non-magnetic V5+.  Our measurements 
  
 
 109 
 
 
 
 
-1.4
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
30 130 230 330 430 530
Temperature, oC
H
e
a
t
 
f
l
o
w
,
 
m
W
.
 
. 160
oC
310oC
330oC
510oC
550oC
 
 
 
 
 
 
Figure 4.8. DSC data for KUVIVP. Several endothermic events between 160 ?C and 550 
?C reveal gradual structural transformations with increase of temperature.  
 
 110 
 
 
 
 
 
 
 
Figure 4.9.  Magnetization of UVVP as a function of applied magnetic field at 5 K.  Line 
is the linear fit to the data. 
 
 111 
 
 
 
 
 
 
 
Figure 4.10. Magnetic susceptibility of UVVP as a function of temperature with a 10000 
G magnetic field. 
 
 112 
indicate that effective moment is smaller than 0.24 B.  If this magnetic contribution is 
arising from a V4+, and the spin only moment of 1.73 B is assumed, then the results are 
consistent with less than 2% of the total V as V4+. 
Magnetization measurements of RbUVIVP, obtained at 5 K, increase linearly with  
magnetic field up to the highest measured field, 10,000 G, as shown in Figure 4.11.  
About 75% of the magnetic signal arises from the background at high temperatures, 
necessitating susceptibility data acquisition in a 10,000 G field.  The temperature 
dependence of the magnetic susceptibility of RbUVIVP, together with its inverse, is 
depicted in Figure 4.12.  The data show complex behavior with temperature.  
Susceptibility data obtained at lower fields, 500 and 2000 Gauss show a similar 
temperature dependence.  The data indicate a long-range ordering of the moments at 
52(2) K. Above that temperature the sample of RbUVIVP appears paramagnetic and the 
data between 100 and 320 K are fit to the modified Curie law and the effective magnetic 
moment is determined to be 1.73(10) mB.  The effective magnetic moment obtained from 
a Curie-Weiss fit to the temperature dependence of inverse magnetic susceptibility is 
1.82(10) mB. The difference between these two values reflects the difference in emphasis 
of the lower or higher temperature data respectively and reflects the inherent error in 
working with such small magnetic signals. cTIP and q  are also determined from the 
modified Curie law fit as -0.00008(4) emu/mole and -41(8) K, respectively.  The large, 
negative Weiss constant is consistent with an antiferromagnetic component to the 
ordering, as is the shape of the c versus T plot.  There is an additional feature in the data 
that occurs at about 15(1) K that could be a re-ordering of the moments as the 
temperature is lowered through the ordered state from 52 K, or it could be a paramagnetic  
 
 113 
 
 
 
 
 
 
 
Figure 4.11. Magnetization of RbUVIVP as a function of applied magnetic field at 5 K.  
Line is the linear fit to the data. 
 
 114 
 
 
 
 
 
Figure 4.12. Magnetic susceptibility of RbUVIVP as a function of temperature.  Line is 
the fit to Curie-Weiss behavior.  Inset shows the temperature dependence of the inverse 
magnetic susceptibility.  
 
 115 
impurity phase. The effective moment at 5 K, determined from the M vs. H curve, is 0.34 
mB.  It is not possible to distinguish between these two options without further studies. 
 Ion-exchange study.  Due to the framework type of the structure, the ion-
exchange experiments were run for both UVVP and KUVIVP. After equilibration of all 
samples of UVVP with NaCl, KCl, CaCl2, SrCl2 solutions the change of the color of 
solutions, decrease of the sample amount, and consequently, the partial dissolution of 
UVVP was detected.  In contrast, the structure of KUVIVP in all exchanged probes, was 
conserved, as was proved by the identity of powder diffraction patterns of the samples, 
tested before and after ion-exchange experiments.  
 There is no uptake of the cations found from the pure 1?10-2 M and 1?10-3 M 
solutions of CaCl2 and SrCl2.  Small exchange was observed in 1?10-2 M NaCl solutions 
with an uptake value 0.25(6) meq/g.  In the mixed 1:1 solutions of NaCl/CaCl2 and 
NaCl/SrCl2 slightly smaller Na+- exchange capacities of 0.18(5) meq/g and 0.17(5) meq/g 
were detected, probably owing not to the competition of Na+/Ca2+ and Na+/Sr2+ cationic 
pairs in the probe, but to the overall dilution of the Na+ solutions.  Ca2+ and Sr2+ uptake 
were not found in the mixed solutions either.   
 Exchange with Cs+ from 1?10-2 M CsCl solution reveals notable uptake 0.87(10) 
meq/g.  The amount of the exchanged Cs+ cations per taken mass of the sample is close to 
50% (46.8%?0.9%) of total cation content, in other words, half of the theoretical 
capacity, calculated from the formula. These results are in good agreement with the 
structural data. We suggest that the larger channels along the a and b axes with size 5.8 ? 
? 4.6 ? and 3.8 ? ?4.6 ?, respectively, are not available for exchange due to the 
presence of undefined electron density, pointed inside of these channels. Therefore, we 
 
 116 
propose that ion-exchange occurs only through smaller channels 2.8 ? ? 4.4 ? along the 
c axis, occupied  by one out of two K+ cations, present in the structure.  The high 
selectivity of the framework toward Cs+ versus K+ can be explained in the radii and 
hydration energy terms.  At the hydrated state the radii of K+ and Cs+ are the same and 
correspond to 3.3 ?.35 Due to the lower dehydration energy Cs+ is able to lose its 
hydration sphere and enter the channels easier than K+.  
 In the mixed Cs+/Na+ solutions with equal concentrations of both cations, again 
only half of the total cation content is exchanged.  Three quarters of exchanged cations 
are Cs+ and only one quarter is Na+. If the concentration of Na+ is doubled in the initial 
mixed solutions, the ratio of exchanged Cs+/Na+ remains the same.  From this data we 
can conclude that KUVIVP is Cs+-selective ion-exchange material with high capacity 
0.87(10) meq/g. 
 
CONCLUSIONS 
 Two novel uranyl vanadium phosphate framework materials have been 
synthesized and studied.  One material is thermally stable up to 500 ?C and demonstrates 
non-linear optical properties. The other exhibits remarkable magnetic properties and 
selective Cs+ uptake from mixed Cs+/Na+ solutions, as would be required by actual 
nuclear waste conditions.  Several issues need to be explained, such as structural 
uncertainty of K(Rb)UVIVP or the reason for the formation of different compounds 
under similar conditions.  We are currently working on the detailed elemental analysis of 
RbUVIVP that will help to solve the structural uncertainties of KUVIVP and RbUVIVP 
members of uranyl vanadium phosphate family.  
 
 117 
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Chemistry , 6th ed.; Wiley-Interscience: New-York, 1999, pp 714-736.  
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561. 
3. Hutchings, G. J. J. Mater. Chem. 2004, 14, 3385. 
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Mater. Chem. 1992, 2, 161. 
9. Obbade, S.;  Dion, C.;  Rivenet, M. ; Saadi, M.;  Abraham F. J. Solid State Chem. 
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10. Obbade, S.; Dion, C.; Saadi, M.; Yagoubi, S.; Abraham, F.  J. Solid State Chem. 
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11. Sykora, R. E.; Albrecht-Schmitt, T. E. Inorg. Chem. 2003, 42, 2179. 
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13. Bayi, F.; Pourroy, G.;  Belaiche, M.; Legall, P.; Drillon, M.; Kuentzler, R. Eur. J. 
Solid State Inorg. Chem. 1993,  30,  55. 
 
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14. Borel, M. M.; Leclaire, A.; Chardon, J.; Michel, C.; Provost, J.; Raveau, B. J. Solid 
State Chem. 1998, 135, 302. 
15. Roca, M.; Amoros, P.; Cano, J.; Marcos, M. D.; Alamo, J.; Beltran-Porter, A.; 
Beltran-Porter, D. Inorg. Chem. 1998, 37, 3167. 
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18. Buehlmann, P.; Pretsch, E.; Bakker, E. Chem. Rev. 1998, 98, 1593. 
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 120 
CHAPTER 5 
HYDROTHERMAL SYNTHESIS AND STRUCTURAL CHARACTERIZATION 
OF Cs1.52[(UO2)(TiOH0.48)(PO4)2]?nH2O and Cs1.35[(UO2)(GeOH0.65)(PO4)2]?nH2O 
 
ABSTRACT 
Two novel uranyl-containing three-dimensional materials 
Cs1.52[(UO2)(TiOH0.48)(PO4)2]?nH2O (UTiP) and Cs1.35[(UO2)(GeOH0.65)(PO4)2]?nH2O 
(UGeP) were synthesized under hydrothermal conditions. The materials are isostructural 
and have identical frameworks, constructed from the perpendicular intersection of one-
dimensional uranyl phosphate and titanium or germanium phosphate chains. The 
channels are occupied by disordered Cs+ cations and disordered water molecules. The 
compounds crystallize in monoclinic space group C2/m. Crystallographic data: UTiP: a  
=  19.715(4) ?, b  =  7.1207(14) ?, c  =  9.4756(19) ?, 
  =  115.93(3)?, V  =  1196.3(4) 
?3, Z = 4, T = 193K. UGeP: a  =  19.5123(17) ?, b  =  6.8639(6)?, c  =  9.3731(8) ?, 
  
=  116.125(2)?, V  =  1127.09(17) ?3, Z = 4, T = 193K.  
 121 
INTRODUCTION 
Potential technical applications of inorganic crystalline three-dimensional 
structures, due to their non-linear optical properties, magnetism, conductivity, or ion-
exchange, leads to a continued search for novel compounds and methods for their 
preparation.1 Three-dimensional uranyl-containing materials have come to the forefront 
because there are thousands of tons of depleted uranium, with very low level radioactivity 
stored at the Savannah River Site and several other locations.  The incorporation of UVI in 
the form of uranyl, UO22+ cations, into crystalline frameworks has the potential of 
yielding functional materials while at the same time expanding our knowledge on the 
crystal chemistry of UVI.  
The formation of uranyl-containing three-dimensional structures is a very 
challenging task due to the reduced dimensionality along axial uranyl-oxygen double 
bonds.29-30 There are several synthetic strategies known today to facilitate the formation 
of frameworks. We focused our study on the incorporation of octahedral building units, 
such as IO65?,28 in order to allow the bond formation in the direction parallel to uranyl 
axis. In previous chapters we have already shown that, indeed, the structure of UGaP125 
and KUVIVP (RbUVIVP)  are formed according to this new synthetic method. In this 
chapter we continue to investigate the conditions of the formation of frameworks by the 
introduction of Ti and Ge coordination polyhedra.  
  The formation of six-coordinate complexes is common in the structural chemistry 
of Ti(IV). In the structures of ETS-4 and ETS-10 molecular sieves,31 Cs+ and Sr2+-
selective titanium silicates Na2Ti2O3(SiO4) H2O and HM3Ti4O4(SiO4) H2O32 and many 
other compounds, as well as in recently synthesized organically templated framework 
 122 
mixed-valent Ti(III)/Ti(IV) phosphates33,34 and mixed-valent Ti(III)/Ti(IV) gallium 
phosphate,35 Ti metal centers form octahedra with different degrees of distortion. In the 
latter structures of TiIIITiIV(PO4)(HPO4)2(H2O)2?0.5NH2CH2CH2CH2NH2, 
TiIIITiIV(HPO4)4?C2N2H9?H2O33,34 and [C5NH6][Ti3Ga(PO4)5(H2O)2]35 both Ti(III) and 
Ti(IV) have a six-folded coordination environment, with small differences in the bond 
length range.  
 The knowledge about crystal chemistry of uranium-titanium oxocompounds is 
restricted to only a series of structures of UTixNb3-xO10 (x = 0.33, 1) and its intercalated 
compound  Li0.9UTiNb2O10, where Ti plays only a substitution role,36 and in several 
mineral structures.37 The most abundant uranium-titanium mineral brannerite, UTi2O6, is 
an important component of the Synroc pyrochlore-type ceramics,38 studied as a storage 
material for Pu isotopes in a geological environment.39, 40 At room temperature naturally 
occurring brannerite is amorphous. It crystallizes only at temperatures above 1000 ?C in 
monoclinic C2/m structure, consisting of layers of titanium edge-sharing octahedra, 
linked together with uranium tetragonal bipyramids.41 One of the proposed mechanisms 
for the stabilization of brannerite-phase formation could be incorporation of doping 
cations such as Ca2+, La3+, and Ga3+ in the structure.42-44 We suggest that the formation of 
crystal structures based on uranium and titanium at hydrothermal temperatures can be 
reached through addition of phosphate groups, which improve the solubility of 
components and stabilize the resultant structure.  
 The coordination polyhedra of germanium can also be used as potential 
octahedral building unit, due to the ability to have coordination numbers 4, 5, or 6, unlike 
its closest neighbor Si.45 This originates from larger Ge, then Si, atomic radius and 
 123 
therefore longer Ge?O bonds and more flexible Ge-O-Ge angle.  The variations in the 
coordination modes of germanium allows it to form structures incorporating 
tetrahedral,46,47 trigonal bipyramidal or square pyramidal48,49 and octahedral50-52  
coordination environments, as well as structures where all three types of polyhedra are 
combined together53-55 and frameworks entirely constructed from germanate units.56-58 
There are a number of features of the germanate frameworks that make this class of 
structures extremely diverse and attractive for detailed studies. First is the ability of 
germanate units to form clusters. [Ge9O18(OH)4] clusters synthesized with different 
organic templates57,59 and  Ge9O19(OH)2(N2C2H10)2(N2C2H8)0.5H2O60 are just a few 
examples of three-dimensional structures with remarkable porosity due to the cluster 
construction. Second, the germanate framework compounds with odd-membered rings 
can be formed.50,52,61,62  Finally, the capacity to build the porous structures with chiral 
channels makes germanates attractive for enantioselective catalysis and separation.60,63,64  
 All known uranyl germanates have layered structures.65,66 The germanate anions 
there exhibit only tetrahedral arrangements. In this chapter, as a continuation of previous 
work, we intend to investigate the potential of Ti and Ge centers to form octahedral 
polyhedra in order to synthesize the first uranyl-containing titanium and germanium 
phosphate framework materials.  
 
EXPERIMENTAL 
Syntheses.  UO2(NO3)2?6H2O (98%, Alfa-Aesar), Ti powder (99.99%, Sigma 
Aldrich), Ge powder (99.99%, Sigma Aldrich), H3PO4 (98%, Aldrich), and CsCl (99.9%, 
Cerac) were used as received. Ti and Ge powder were handled in the glovebox under an 
 124 
Ar atmosphere due to the potential rapid oxidation in air. For all reactions PTFE-lined 
Parr 4749 vessels were loaded with reaction mixture and 1 mL of distilled and Millipore 
filtered water with a resistance of 18.2 MW?cm. Despite the presence of only depleted 
uranium in UO2(NO3)2?6H2O and products of the reactions, and therefore very low level 
of radioactivity, all studies were carried out with precautions. Semi-quantitative 
SEM/EDX analyses were performed using a JEOL JSM-7000F instrument.  Cs, U, Ti, 
Ge, and P percentages were calibrated against standards.    
Cs1.52[(UO2)(TiOH0.48)(PO4)2]?nH2O (UTiP).  UO2(NO3)2?6H2O  (0.276 g, 0.549 
mmol),  H3PO4 (0.161 g, 1.64 mmol) and CsCl (0.554 g, 2.75 mmol) were combined 
together in 23 mL PTFE liner with 1 mL of water with stirring until homogenous. The Ti 
(0.026g, 0.55 mmol) was quickly added to the reaction mixture, the autoclave was rapidly 
sealed, placed in a box furnace, and heated at 195 ?C for seven days. Then reaction was 
slowly cooled with an average rate 1 ?C/hour. The solid part of the product mixture was 
washed with water and methanol and dried in air. The final composition of the mixture 
was identified as small fractions of pale yellow crystals of UTiP, mixed together with 
yellow crystals of uranyl phosphate and excess Ti metal, and larger portions of 
amorphous UTiP.  The isolated yield of crystalline UTiP was 0.028 g (7.1 % yield based 
on the U).  EDX analysis provided Cs:U:Ti:P ratio of 1.5:1:1:2. 
Cs1.35[(UO2)(GeOH0.65)(PO4)2]?nH2O (UGeP). UO2(NO3)2?6H2O  (0.282 g, 
0.561 mmol),  H3PO4 (0.165 g, 1.64 mmol) and CsCl (0.472 g, 2.81 mmol) were mixed in 
a 23 mL PTFE-lined autoclave with 1 mL of water and Ge (0.081 g, 1.1 mmol) powder, 
weighed separately in the glovebox.. The sealed vessel was heated at 195 ?C for five days 
and cooled to room temperature at the rate of 9?C/hour. After decantation of the mother 
 125 
liquid small yellow crystals of UGeP, grown on the surface of non-crystalline product 
were found. The yield of UGeP was near quantitative. EDX analysis provided Cs:U:Ge:P 
ratio of 1.5:1:1:2. 
Crystallographic Studies.  Crystals of UTiP and UGeP were mounted on glass 
fibers and aligned on a Bruker SMART APEX CCD X-ray diffractometer.  Intensity 
measurements were performed using graphite monochromated Mo Ka radiation from a 
sealed tube and monocapillary collimator.  SMART (v 5.624) was used for preliminary 
determination of the cell constants and data collection controls.  The intensities of 
reflections of a sphere were collected by a combination of 3 sets of exposures (frames).  
Each set had a different f angle for the crystal and each exposure covered a range of 0.3? 
in w.  A total of 1800 frames were collected with an exposure time per frame of 120 s for 
both UTiP and UGeP due to the extremely small dimensions of the crystals.  
 Determination of integrated intensities and global refinement were performed 
with the Bruker SAINT (v 6.02) software package using a narrow-frame integration 
algorithm.  A face-indexed analytical absorption correction was initially applied using 
XPREP, where individual shells of unmerged data were corrected analytically.67  These 
files were subsequently treated with a semiempirical absorption correction by 
SADABS.68  The program suite SHELXTL (v 6.12) was used for space group 
determination (XPREP), direct methods structure solution (XS), and least-squares 
refinement (XL).67  The final refinements included anisotropic displacement parameters 
for all atoms.  Secondary extinction was not noted for either crystal.  Some 
crystallographic details are given in Table 5.1. Atomic coordinates and displacement 
parameters for all atoms of UTiP can be found in Table 5.2, UGeP ? in Table 5.3.  
 126 
Table 5.1. Crystallographic Data for Cs1.52[(UO2)(TiOH0.48)(PO4)2]?nH2O (UTiP) and 
Cs1.35[(UO2)(GeOH0.65)(PO4)2]?nH2O (UGeP). 
Compound UTiP UGeP 
Formula Mass 740.16 742.28 
Color and habit yellow plate yellow plate 
Crystal System Monoclinic Monoclinic 
Space group C2/m (No. 12) C2/m (No. 12) 
a (?) 19.715(4) 19.5123(17) 
b (?) 7.1207(14) 6.8639(6) 
c (?) 9.4756(19) 9.3731(8) 

 (?) 115.93(3) 116.125(2) 
V (?3) 1196.3(4) 1127.09(17) 
Z 4 4 
T (K) 193 193 
l (?) 0.71073 0.71073 
Maximum 2q (deg.) 56.64 56.52 
rcalcd (g cm?3) 4.110 4.374 
m(Mo Ka) (cm?1) 190.8 213.6 
R(F) for Fo2 > 2s(Fo2)  0.0371 0.0412 
Rw(Fo2) b 0.0747 0.0977 
a ( )R F F F F= -
 

o c o .  
b ( ) ( )R F w F F wF
w o
2
o
2
c
2 2
o
4
1 2
= - 
 
  . 
 
 
 
 
 127 
Table 5.2.  Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 
Cs1.52[(UO2)(TiOH0.48)(PO4)2]?nH2O (UTiP). 
Atom Symmetrya x y z Ueq (?2) b s.o.f. 
U(1) 4  i  m 0.04052(2) 0 -0.66748(5) 0.0109(1) 1 
Ti(1) 4  e  1 ? ? 0 0.0156(4) 1 
P(1) 4  i  m 0.12604(16) 0 -0.9415(3)) 0.0115(6) 1 
P(2) 4  i  m 0.15447(16) 0 -0.3148(3) 0.0115(6) 1 
O(1) 4  i  m 0.1665(5) 0 -0.4635(9) 0.027(2) 1 
O(2) 8  j  1 0.1866(4) 0.1742(8) -0.2172(7) 0.0287(15) 1 
O(3) 4  i  m 0.0670(4) 0 -0.3835(9)) 0.024(2) 1 
O(4) 4  i  m -0.0517(5) 0 -0.9137(10) 0.037(2) 1 
O(5) 4  i  m 0.1134(5) 0 -0.7976(10) 0.037(3) 1 
O(6) 8  j  1 0.0413(4) 0.2490(8) -0.6652(7) 0.0269(14) 1 
O(7) 8  j  1 0.1715(3) 0.1769(8) -0.9408(8) 0.0295(16) 1 
O(8) 4  i  m 0.2912(4) 0 -0.9540(9) 0.0139(16) 1 
O(9) 4  i  m 0.3640(7) 0 -0.2041(17) 0.047(5) 0.85(3) 
Cs(1) 4  i  m 0.30542(5) 0 -0.5527(1) 0.0289(3) 0.874(3) 
Cs(2) 4  i  m 0.4233(3) 0 -0.6394(7) 0.046(2) 0.194(4) 
Cs(3) 4  i  m 0.45520(11) 0 0.0264(3) 0.0405(8) 0.457(3) 
a Symmetry describes multiplicity, Wyckoff parameter and symmetry of the atomic site. 
b Ueq is defined as one-third of the trace of the orthogonalized Uij tensor. 
 128 
Table 5.3.  Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 
Cs1.35[(UO2)(GeOH0.65)(PO4)2]?nH2O (UGeP). 
Atom Symmetrya x y z Ueq (?2) b s.o.f. 
U(1) 4  i  m 0.04126(2) 0.0000 -0.66805(5) 0.00962(15) 1 
Ge(1) 4  e  1 ? ? 0 0.0174(3) 1 
P(1) 4  i  m 0.12860(19) 0 -0.9417(4) 0.0128(6) 1 
P(2) 4  i  m 0.15654(18) 0 -0.3081(4) 0.0110(6) 1 
O(1) 4  i  m 0.1692(6) 0 -0.4552(11) 0.027(2) 1 
O(2) 8  j  1 0.1886(6) 0.1811(11) -0.2092(9) 0.050(3) 1 
O(3) 4  i  m 0.0689(6) 0 -0.3787(12) 0.055(5) 1 
O(4) 4  i  m -0.0523(7) 0 -0.9147(13) 0.052(4) 1 
O(5) 4  i  m 0.1180(6) 0 -0.7930(12 0.057(5) 1 
O(6) 8  j  1 0.0404(4) 0.2571(12) -0.6643(11) 0.042(2) 1 
O(7) 8  j  1 0.1756(6) 0.1797(12) -0.9392(17) 0.060(3) 1 
O(8) 4  i  m 0.2929(6) 0 -0.9512(11) 0.020(2) 1 
O(9) 4  i  m 0.3707(17) 0 -0.186(3) 0.062(10) 0.63(7) 
Cs(1) 4  i  m 0.30512(7) 0 -0.54392(16) 0.0383(5) 0.812(6) 
Cs(2) 4  i  m 0.4159(11) 0 -0.682(2) 0.069(7) 0.100(7) 
Cs(3) 4  i  m 0.45559(14) 0 0.0046(4) 0.0396(10) 0.435(5) 
a Symmetry describes multiplicity, Wyckoff parameter and symmetry of the atomic site. 
b Ueq is defined as one-third of the trace of the orthogonalized Uij tensor. 
 
 
 
 
 
 129 
RESULTS AND DISCUSSION 
Syntheses.  The syntheses of UTiP and UGeP appear to be similar and yield 
isostructural compounds. Both Ti and Ge starting materials are pure elements. Ti powder 
was previously used in the production of several titanium phosphates,33-35 which often led 
to the partial oxidation of titanium and synthesis of mixed-valent materials. UTiP also 
could be synthesized from titanium isopropoxide Ti(OC3H7)4 as a source of Ti, but 
crystals were very small and could be seen only using SEM. We speculated that the 
choice of the source material can play a crucial role in crystal growth.  In the study of 
synthetic conditions for the formation of jarosites, Grohol and Nocera68 suggested that 
slow oxidation of vanadium metal can be the rate-determining step in the crystallization 
of the final vanadium sulfate mineral. This could also be true for the development of 
UTiP and UGeP as well. Slow delivery of oxidized reactants to the reaction mixture of 
uranyl nitrate and phosphoric acid aids in the formation of a multicomponent system 
instead of separate titanium or germanium phosphates and uranyl phosphate, and gives 
the possibility of growing crystals with dimensions acceptable for single-crystal X-ray 
diffraction.  
Structure. The crystallographic data (Table 5.1) and atomic coordinates (Tables 
5.2 and 5.3) of Cs1.52[(UO2)(TiOH0.48)(PO4)2]?nH2O (UTiP) and  
Cs1.35[(UO2)(GeOH0.65)(PO4)2]?nH2O (UGeP) are closely related. This indicates that 
UTiP and UGeP are isostructural compounds. The variation in the b axis of the unit cell 
(7.1207 ? for UTiP and 6.8639 ? for UGeP) can be explained in the terms of  ionic radii 
of Ti+4 (0.61 ?) and Ge+4 (0.39 ? ) and, indeed, corresponds to the difference in the radii 
and average difference between Ti-O and Ge-O bond length (1.939 ? and 1.856 ? 
 130 
respectively).  
 The structures of UTiP and UGeP are closely related to the structure of 
Cs4[(UO2)2(GaOH)2(PO4)4]?H2O,25 described in Chapter 3. In general, it is a framework 
structure, built out of perpendicularly intersecting one-dimensional uranyl phosphate and 
titanium or germanium phosphate chains. The channels, formed along the c axis, are 
filled with Cs+ cations. The fundamental building unit of UTiP (or UGeP) is shown in 
Figure 5.1.  
 Uranyl phosphate chains of UTiP and UGeP extended in the c direction, and have 
the same topology as uranyl phosphate chains in the structures of 
Cs4[(UO2)2(GaOH)2(PO4)4]?H2O and Cs[UO2Ga(PO4)2]25. (Figure 5.2) These chains have 
been previously described as 1? [UO2(PO4)2]4-25,70 They differ from 
Cs4[(UO2)2(GaOH)2(PO4)4]?H2O, in that there are two crystallographically unique 
uranium centers. In UTiP and UGeP structures only one unique uranium is present, and 
therefore only one uranyl phosphate chain is formed. This phenomenon can also be 
secondarily confirmed by the unit cell comparison.  In Cs4[(UO2)2(GaOH)2(PO4)4]?H2O, 
the dimension of the unit cell axis, containing two crystallographycally unique uranyl 
phosphate chains, is doubled compare to UTiP and UGeP .  
 The uranium center is connected to five phosphate oxygen atoms in the equatorial 
plane and two uranyl oxygen atoms, almost linearly with angles 178.7(4)? and 177.1(7)? 
for UTiP and UGeP, respectively, in the axial direction, to form a pentagonal bipyramid 
environment. The U-O distances in the equatorial plane are long and range between  
 
 
 131 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 5.1.  Thermal ellipsoid plot of Cs1.52[(UO2)(TiOH0.48)(PO4)2]?nH2O (UTiP) shown 
at 50% probability.   
 
 132 
 
 
 
 
 
 
 
 
 
Figure 5.2 Depiction of one-dimensional titanium phosphate or germanium phosphate 
(top) and uranyl phosphate (bottom) chains in UTiP or UGeP. Violet - titanium or 
germanium polyhedra, yellow-phosphate tetrahedra, green-uranyl building units. 
 133 
2.245(9) ? and 2.507(8) ? for UTiP and between 2.227(11) ? and 2.521(10) ? for 
UGeP, compared to the short uranyl distances of 1.773(6) ? for UTiP and 1.765(8) ? for 
UGeP. Two uranyl pentagonal bipyramids share edges to form dimers, connected to the 
chain by phosphate anions. The bond-valence sums, calculated according to these data, 
correspond to uranium in the +6 oxidation state. 
  Titanium and germanium phosphate chains 1? [Ti(OH0.48)(PO4)2]2? and 
1
? [Ge(OH0.65)(PO4)2]
2?, are also very similar to gallium phosphate chain in 
Cs4[(UO2)2(GaOH)2(PO4)4]?H2O.25  Titanium and germanium each form bonds with six 
oxygen atoms, four from phosphate anions and two from the neighbouring titanium or 
germanium unit,  in octahedral environments. Due to the difference in the ionic size of 
Ti(IV) and Ge(IV), as well as the nature of the orbitals, participating in the bond 
formation, Ti-O and Ge-O distances are different. For Ti-O, the distances range from 
1.926 ? to 1.960 ?, which is within the normal distance range for Ti in an octahedral 
environment. In the different Ge octahedra, Ge-O bonds vary from 1.77 ? to 2.06 ?, and 
again bond lengths in UGeP fit in this range. These distances are also much longer than 
Ge-O distances in the tetrahedra, where they can range between 1.70 ? and 1.79 ?. The 
bond-valence sums are consistent with Ti and Ge present in a +4 oxidation state. Selected 
bond distances and angles for UTiP and UGeP are summarized in Tables 5.4 and 5.5. 
 The intersection of the uranyl phosphate chains, extended in the c direction, and 
titanium or germanium phosphate chains, run along the b axis, giving rise to the tunnels 
filled with Cs+ cations. (Figure 5.3) There are four strongly disordered atomic sites in the 
channels. According to the refinement of occupancy of these atomic sites, we suggest that 
 134 
Table 5.4. Selected Bond Distances (?) and Angles (?) for 
Cs1.52[(UO2)(TiOH0.48)(PO4)2]?nH2O (UTiP) 
Distances (?) 
U(1)-O(6)  1.773(6) Ti(1)-O(2) 1.960(6) 
U(1)-O(4) 2.245(9) P(1)-O(5) 1.490(9) 
U(1)-O(5) 2.265(8) P(1)-O(4) 1.508(9) 
U(1)-O(3) 2.371(8) P(1)-O(7) 1.545(6) 
U(1)-O(1) 2.389(8) P(2)-O(1) 1.511(6) 
U(1)-O(3?) 2.507(8) P(2)-O(2) 1.528(8) 
Ti(1)-O(8) 1.926(3) P(2)-O(3) 1.555(8) 
Ti(1)-O(7) 1.933(6)   
Angles (?) 
O(6)?U(1)?O(6?)  178.7(4) O(7)?Ti(1)?O(7?) 180.00(15) 
O(8)?Ti(1)?O(8?) 180.0(5) O(2)?Ti(1)?O(2?) 180.000(2) 
 
 
 
 
 
 
 
 
 
 
 135 
Table 5.5. Selected Bond Distances (?) and Angles (?) for 
Cs1.35[(UO2)(GeOH0.65)(PO4)2]?nH2O (UGeP) 
Distances (?) 
U(1)-O(6)  1.765(8) Ge(1)-O(2) 1.853(7) 
U(1)-O(4) 2.227(11) P(1)-O(5) 1.497(10) 
U(1)-O(5) 2.271(10) P(1)-O(4) 1.505(12) 
U(1)-O(3) 2.376(10) P(1)-O(7) 1.531(8) 
U(1)-O(1) 2.414(10) P(2)-O(2) 1.512(8) 
U(1)-O(3?) 2.521(10) P(2)-O(1) 1.504(10) 
Ge(1)-O(8) 1.875(4) P(2)-O(3) 1.538(11) 
Ge(1)-O(7) 1.842(8)   
Angles (?) 
O(6)?U(1)?O(6?)  177.1(7) O(7)?Ge(1)?O(7?) 180.0(3) 
O(8)?Ge(1)?O(8?) 180.000(1) O(2)?Ge(1)?O(2?) 180.000(2) 
 
 
 
 
 
 
 
 
 
 
 136 
 
 
 
 
 
 
 
 
 
 
Figure 5.3. The framework of UTiP and UGeP. The channels along the c axis are filled 
with Cs+ cations (purple) and water molecules (red). Violet octahedra represent Ti or Ge, 
yellow ? phosphate, and green ? uranium centers.  
 137 
three partially occupied Cs+ cations reside in the channels with Cs-O distances ranging  
from 3.029(8) ? to 3.6172(17) ? for UTiP and from 2.856(15) ? to 3.631(10) ? for 
UGeP. The fourth electron density peak is assigned to the partially occupied water 
molecule. It is 0.85 water molecules per unit cell for UTiP and 0.63 for UGeP. Due to 
the incompletely filled Cs positions, the overall structure has a positive charge deficiency. 
This can be balanced by protonation of the titanium phosphate or germanium phosphate 
backbone. The bond-valence sum for O(8) corresponds to 1.38 and 1.42 for UTiP and 
UGeP, respectively, which is consistent with the degree of protonation in these 
structures. This type of protonation is also found in aluminophosphate mineral tancoite, 
LiNa2H[Al(PO4)2(OH)],71,72 Cs4[(UO2)2(GaOH)2(PO4)4]?H2O25 and large number of 
aluminum, gallium, and transition metal phosphates.73-80 It is important to note that in 
Cs4[(UO2)2(GaOH)2(PO4)4]?H2O25 and LiNa2H[Al(PO4)2(OH)],71,72  protons are assigned 
to stabilize the structure with Ga and Al in oxidation state +3, but in the case of UTiP and 
UGeP, the proton?s role is restricted only to equilibrate the Cs+ cations deficiency.   
 
CONCLUSIONS 
 In this chapter we have described two novel isostructural uranium-containing 
framework compounds incorporating Ti or Ge polyhedra. According to the structural 
characterization, we can imply that these compounds can have promising ion-exchange 
and conductivity properties due to the presence of highly disordered cationic sites.  For 
further investigations, more detailed analysis of the Cs and water content, as well as 
knowledge about physical properties of structure are necessary. We are currently 
 138 
investigating the methods for the synthesis of UTiP and UGeP with higher yields that 
will allow us to conduct detailed studies of the compounds.    
 139 
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 144 
CHAPTER 6 
GENERAL ROUTE TO THREE-DIMENSIONAL FRAMEWORK URANYL 
TRANSITION METAL PHOSPHATES WITH ATYPICAL STRUCTURAL 
MOTIFS: THE CASE EXAMPLES OF Cs2{(UO2)4[Co(H2O)2]2(HPO4)(PO4)4}, 
Cs2{(UO2)4[Ni(H2O)2]2(HPO4)(PO4)4} AND Cs3+x[(UO2)3CuH4-x(PO4)5]?H2O 
 
ABSTRACT 
 The reaction of UO2(NO3)2?6H2O with Co, Ni, or Cu metal, phosphoric acid, and 
CsCl under mild hydrothermal conditions results in the formation of 
Cs2{(UO2)4[Co(H2O)2]2(HPO4)(PO4)4} (UCoP),  Cs2{(UO2)4[Ni(H2O)2]2(HPO4)(PO4)4} 
(UNiP) or Cs3+x[(UO2)3-xCuH4-x(PO4)5]?H2O (UCuP).  UCoP and UNiP are isostructural 
compounds.  Their structures contain uranium atoms in pentagonal bipyramidal and 
hexagonal bipyramidal environments.  The interaction of the uranyl cations and 
phosphate anions creates layers in the [ab] plane.  The uranyl phosphate layers are joined 
together by octahedral Co or Ni centers wherein the Co and Ni are bound by phosphate 
and two cis water molecules.  In addition, the Co and Ni ions are also ligated by a uranyl 
oxo atom.  The presence of these octahedral building units stitches the structure together 
into a three-dimensional framework where void spaces are filled by Cs+ cations. 
 The structure of UCuP contains uranium centers in UO6 tetragonal bipyramidal 
and UO7 pentagonal bipyramidal geometries.  The uranyl moieties are bridged by 
 145 
phosphate anions into sinusoidal sheets that extend into the [bc] plane and are linked into 
a three-dimensional structure by CuII.  The Cu centers reside in square planar 
environments.  Charge balance is maintained by Cs+ cations. Both the structure types and 
the uranyl phosphate layers in UCoP, UNiP, and UCuP are novel. 
 
INTRODUCTION 
 The structural chemistry of UVI is dominated by the formation of layered 
compounds containing uranyl, UO22+, cations wherein the uranyl units are aligned in a 
roughly parallel fashion.1,2  These layered compounds have been shown to display several 
important and potentially useful properties including fast proton conductivity and ion 
exchange that is particularly well-known for uranyl phosphates.3-8 More recently, 
attention has been focused on preparing uranyl phases that adopt three-dimensional 
networks that may find applications in the storage of key radionuclides from spent 
nuclear fuel and as new selective ion-exchange materials.9  One of the most appealing 
features of constructing new solids from uranyl-containing polyhedra is that the uranium 
centers in these compounds can adopt coordination environments seldom seen in 
transition metal chemistry such as UO7 pentagonal bipyramids and UO8 hexagonal 
bipyramids.1,2 
 In previous chapters we have reported the syntheses and structures of the first 
uranyl gallium,9 vanadium,10 titanium and germanium phosphates with open-framework 
structures.  As we demonstrated, UGaP1, UGaP2, and KUVIVP (RbUVIVP) have ion-
exchange properties.  Herein we have devoted our research to preparing additional first 
row transition metal uranyl phosphates where the gallium, germanium, vanadium, or 
 146 
titanium centers have been replaced by other transition metals, which may, in turn, lead 
to new architectures, and, therefore, to properties, not previously found.  We also report a 
relatively general and quite facile route to preparing first row transition metal uranyl 
phosphates with three-dimensional structures with varying degrees of openness.  We 
illustrate this with the examples of the CoII, NiII, and CuII compounds, 
Cs2{(UO2)4[Co(H2O)2]2(HPO4)(PO4)4} (UCoP),  Cs2{(UO2)4[Ni(H2O)2]2(HPO4)(PO4)4} 
(UNiP) or Cs3+x[(UO2)3-CuH4-x(PO4)5]?H2O (UCuP), all three of which display new 
methods of constructing three-dimensional uranyl-containing frameworks.11-22 
 
EXPERIMENTAL 
Syntheses. UO2(NO3)2?6H2O (98%, Alfa-Aesar), Co powder (99.99%, Sigma 
Aldrich), Ni powder (99.99%, Sigma Aldrich), Cu powder (99.99%, Sigma Aldrich), 
H3PO4 (98%, Aldrich), and CsCl (99.9%, Cerac) were used as received.  Co, Ni, and Cu 
powders were weighed separately under the inert atmosphere due to their potential rapid 
oxidation in the air. The  PTFE liners were used for all reactions. While the UO3 contains 
depleted U, standard precautions for handling radioactive materials should be followed.  
Old sources of depleted U should not be used, as the daughter elements of natural decay 
are highly radioactive and present serious health risks.    
Cs2{(UO2)4[Co(H2O)2]2(HPO4)(PO4)4} (UCoP). UO2(NO3)2?6H2O (0.285 g, 
0.568 mmol), Co powder (0.067 g, 1.1 mmol), H3PO4 (0.167 g, 1.72 mmol), CsCl (0.479 
g, 2.85 mmol), and 1.5 mL of Millipore-filtered water were loaded into a 23-mL 
autoclave. The reaction was run at 195 ?C in a box furnace for 7 days and then cooled at a 
rate of 9 ?C/h to room temperature.  The product mixture contained bright-orange crystals 
 147 
of UCoP and water-soluble blue crystals of cesium tetrachlorocobalt(II).  The desired 
product was isolated by washing the mixture with water and methanol. Yield: 0.286 mg 
(100% based on U).  
 Cs2{(UO2)4[Ni(H2O)2]2(HPO4)(PO4)4} (UNiP). UO2(NO3)2?6H2O (0.286 g, 0.57 
mmol), Ni powder (0.067 g, 1.1 mmol), H3PO4 (0.167 g, 1.72 mmol) and CsCl (0.479 g, 
2.85 mmol), were mixed together in a 23-mL autoclave and followed by addition of 1.5 
mL of Millipore-filtered water.  The reaction was run at 195 ?C in a box furnace for 5 
days and then slowly cooled to room temperature with average rate 3?C/hour.  The 
product mixture contained precipitate of greenish-yellow plates of UNiP and bright green 
mother liquid.  UNiP precipitate was washed with water, methanol and dried by air. 
Yield: 285 mg (82.4 % based on U). 
 Cs3+x[(UO2)3CuH4-x(PO4)5]?H2O (UCuP).  UO2(NO3)2?6H2O (0.285 g, 0.567 
mmol), Cu powder (0.072 g, 1.1 mmol), H3PO4 (0.167 g, 1.72 mmol) and CsCl (0.477 g, 
2.85 mmol), were mixed together in a 23-mL autoclave followed by addition of 1.5 mL 
of Millipore-filtered water.  The reaction was run at 220 ?C in a box furnace for 7 days 
and then cooled at a rate of 9 ?C/h to room temperature.  Due to the large size of the 
crystals, green UCuP product was easily separated from the product mixture, that also 
included also crystals of cesium tetrachlorocopper and cesium uranyl pyrophosphate.  
Yield: 330 mg (97.6 % based on U). 
X-ray structural analysis.  Crystals of UCoP, UNiP, and UCuP were mounted 
on glass fibers and aligned on a Bruker SMART APEX CCD X-ray diffractometer.  
Intensity measurements were performed using graphite monochromated Mo Ka radiation 
from a sealed tube and monocapillary collimator.  SMART (v 5.624) was used for 
 148 
preliminary determination of the cell constants and data collection control.  The 
intensities of reflections of a sphere were collected by a combination of 3 sets of 
exposures (frames).  Each set had a different f angle for the crystal and each exposure 
covered a range of 0.3? in w.  A total of 1800 frames were collected with an exposure 
time per frame of 30 s for the crystals of UCoP, UNiP, and UCuP.  
 Determination of integrated intensities and global refinement were performed 
with the Bruker SAINT (v 6.02) software package using a narrow-frame integration 
algorithm.  A face-indexed analytical absorption correction was initially applied using 
XPREP, where individual shells of unmerged data were corrected analytically.23  These 
files were subsequently treated with a semiempirical absorption correction by 
SADABS.24  The program suite SHELXTL (v 6.12) was used for space group 
determination (XPREP), direct methods structure solution (XS), and least-squares 
refinement (XL).23  The final refinements included anisotropic displacement parameters 
for all atoms.  Secondary extinction was not noted for either crystal.  Crystallographic 
details are given in Table 6.1. Atomic coordinates, equivalent isotropic displacement 
parameters, symmetry and occupancy for UCoP, UNiP, and UCuP are given in Tables 
6.2, 6.3, and 6.4 respectively. 
 Thermal analysis. The data were collected using differential scanning 
calorimeter TA Instrument, model 2920.  The samples of known mass encapsulated in the 
aluminum container, was heated under nitrogen atmosphere from 30 ?C to 600 ?C with 
heating rate of 10?C /minute.  
Table 6.1. Crystallographic Data for Cs2{(UO2)4[Co(H2O)2]2(HPO4)(PO4)4} (UCoP), 
Cs2{(UO2)4[Ni(H2O)2]2(HPO4)(PO4)4} (UNiP) and Cs3+x[(UO2)3CuH4-x(PO4)5]?H2O 
 149 
(UCuP).  
Compound UCoP UNiP UCuP 
Formula Mass 2003.65 2003.21 1788.35 
Color and habit orange plate yellow-green green plate 
Crystal System monoclinic monoclinic orthorhombic 
Space group C2/c (No.15 ) C2/c (No.15 ) Pbcm (No. 57) 
a (?) 18.0551(8) 18.0443(13) 7.5867(4) 
b (?) 10.7478(5) 10.7375(8) 19.9574(10) 
c (?) 15.3504(7) 15.2268(11) 17.9726(9) 

 ?, C 99.2420(10) 99.1520(10) 90 
V (?3) 2940.1(2) 2912.6(4) 2721.2(2) 
Z 4 4 4 
T (K) 193 193 193 
l (?) 0.71073 0.71073 0.71073 
Maximum 2q(deg.)  56.56 56.58 56.58 
rcalcd (g cm?3) 4.524 4.595 4.348 
m(Mo Ka) (cm?1) 258.86 262.82 231.04 
R(F) for Fo2 > s(Fo2) 0.0281 0.0319 0.0354 
Rw(Fo2) b 0.0692 0.0709 0.0835 
a ( )R F F F F= -
 

o c o .  
b ( ) ( )R F w F F wF
w o
2
o
2
c
2 2
o
4
1 2
= - 
 
  . 
 
 
Table 6.2.  Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 
 150 
Cs2{(UO2)4[Co(H2O)2]2(HPO4)(PO4)4} (UCoP). 
Atom Symmetrya x y z Ueq (?2) b Occup. 
U(1) 4  e 2 0 -0.28631(3) ? 0.00974(9) 1 
U(2) 4  e 2 0 0.09385(3) ? 0.00892(9) 1 
U(3) 8  f  1 0.20409(1) 0.28203(2) 0.29034(2) 0.00778(7) 1 
Co(1) 8  f  1 0.21057(5) 0.33986(9) 0.05694(6) 0.01051(19) 1 
P(1) 8  f  1 0.0001(2) 0.3800(3) 0.2841(3) 0.0104(7) 0.50 
P(2) 8  f  1 0.34785(10) 0.44837(16) 0.20623(12) 0.0085(3) 1 
P(3) 8  f  1 0.31032(10) 0.10909(16) 0.15358(12) 0.0079(3) 1 
O(1) 4  e 2 0 0.4966(8) ? 0.069(4) 1 
O(2) 8  f  1 -0.0192(6) 0.4143(9) 0.3795(7) 0.012(2) 0.50 
O(3) 8  f  1 0.0647(3) 0.2934(5) 0.2844(6) 0.045(2) 1 
O(4) 8  f  1 0.4309(3) 0.4041(4) 0.2155(3) 0.0102(10) 1 
O(5) 8  f  1 0.3640(3) 0.5903(4) 0.2212(3) 0.0096(10) 1 
O(6) 8  f  1 0.3115(3) 0.3939(4) 0.2801(3) 0.0091(10) 1 
O(7) 8  f  1 0.3057(3) 0.4264(5) 0.1153(3) 0.0125(10) 1 
O(8) 8  f  1 0.2775(3) 0.1403(5) 0.2362(3) 0.0113(10) 1 
O(9) 8  f  1 0.3140(3) -0.0325(4) 0.1410(3) 0.0111(10) 1 
O(10) 8  f  1 0.2604(3) 0.1628(5) 0.0701(3) 0.0102(10) 1 
O(11) 8  f  1 0.3897(3) 0.1638(5) 0.1593(3) 0.0118(10) 1 
O(12) 8  f  1 0.0407(3) -0.2874(6) 0.1515(4) 0.0260(14) 1 
O(13) 8  f  1 0.1595(3) 0.5213(5) 0.0361(4) 0.0232(13) 1 
O(14) 8  f  1 0.1051(3) 0.2584(5) 0.0071(3) 0.0164(11) 1 
O(15) 8  f  1 0.2387(3) 0.2303(5) 0.3998(3) 0.0129(10) 1 
O(16) 8  f  1 0.1722(3) 0.3329(5) 0.1793(3) 0.0141(10) 1 
O(17) 8  f  1 0.0092(3) 0.0926(5) 0.1371(4) 0.0160(11) 1 
 151 
Cs(1) 8  f  1 0.37456(3) 0.44843(6) 0.47121(3) 0.02451(13) 1 
a Symmetry describes multiplicity, Wyckoff parameter and symmetry of the atomic site. 
b Ueq is defined as one-third of the trace of the orthogonalized Uij tensor. 
 152 
Table 6.3.  Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 
Cs2{(UO2)4[Ni(H2O)2]2(HPO4)(PO4)4} (UNiP). 
Atom Symmetrya x y z Ueq (?2) b occup. 
U(1) 4  e 2 0 -0.28780(4) ? 0.01120(11) 1 
U(2) 4  e 2 0 0.09224(4) ? 0.00986(11) 1 
U(3) 8  f  1 0.20419(2) 0.28060(3) 0.29040(2) 0.00887(9) 1 
Ni(1) 8  f  1 0.21041(6) 0.33766(10) 0.05657(7) 0.0109(2) 1 
P(1) 8  f  1 0.0001(2) 0.3792(4) 0.2849(3) 0.0130(9) 0.50 
P(2) 8  f  1 0.34763(12) 0.4467(2) 0.20535(15) 0.0094(4) 1 
P(3) 8  f  1 0.31001(12) 0.1083(2) 0.15224(15) 0.0093(4) 1 
O(1) 4  e 2 0 0.4951(11) ? 0.062(4) 1 
O(2) 8  f  1 -0.0180(7) 0.4136(10) 0.3857(11) 0.026(3) 0.50 
O(3) 8  f  1 0.0647(4) 0.2910(6) 0.2841(7) 0.044(3) 1 
O(4) 8  f  1 0.4311(3) 0.4027(5) 0.2147(4) 0.0115(12) 1 
O(5) 8  f  1 0.3642(3) 0.5885(5) 0.2204(4) 0.0123(13) 1 
O(6) 8  f  1 0.3121(3) 0.3919(5) 0.2799(4) 0.0113(12) 1 
O(7) 8  f  1 0.3053(3) 0.4240(5) 0.1136(4) 0.0139(13) 1 
O(8) 8  f  1 0.2771(3) 0.1380(5) 0.2358(4) 0.0133(13) 1 
O(9) 8  f  1 0.3143(3) -0.0340(5) 0.1390(4) 0.0112(12) 1 
O(10) 8  f  1 0.2600(3) 0.1629(5) 0.0691(4) 0.0104(12) 1 
O(11) 8  f  1 0.3894(3) 0.1632(5) 0.1582(4) 0.0119(12) 1 
O(12) 8  f  1 0.0405(4) -0.2884(7) 0.1508(4) 0.0247(16) 1 
O(13) 8  f  1 0.1591(3) 0.5150(6) 0.0383(4) 0.0185(14) 1 
O(14) 8  f  1 0.1075(3) 0.2553(6) 0.0084(4) 0.0159(14) 1 
O(15) 8  f  1 0.2389(3) 0.2285(5) 0.4004(4) 0.0155(13) 1 
O(16) 8  f  1 0.1732(3) 0.3316(6) 0.1779(4) 0.0151(13) 1 
 153 
O(17) 8  f  1 0.0102(3) 0.0921(6) 0.1360(4) 0.0165(14) 1 
Cs(1) 8  f  1 0.37476(3) 0.44631(6) 0.47172(4) 0.02446(15) 1 
a Symmetry describes multiplicity, Wyckoff parameter and symmetry of the atomic site. 
b Ueq is defined as one-third of the trace of the orthogonalized Uij tensor. 
 154 
Table 6.4.  Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 
Cs3+x[(UO2)3CuH4x(PO4)5]?H2O (UCuP). 
Atom Symmetrya x y z Ueq (?2) b Occup. 
U(1) 4  d  ..m -0.50309(5) 0.39763(2) ? 0.01050(10) 1 
U(2) 8  e  1 0.21145(4) 0.65898(1) 0.55377(2) 0.00997(9) 1 
Cu(1) 4  d  ..m 0.00099(18) 0.40714(6) ? 0.0115(3) 1 
P(1) 4  d  ..m 0.1054(4) 0.66578(14) ? 0.0140(6) 1 
P(2) 8  e  1 0.2132(3) 0.48119(10) 0.62264(11) 0.0132(4) 1 
P(3) 8  e  1 0.2080(3) 0.66171(10) 0.38077(11) 0.0121(4) 1 
O(1) 4  d  ..m -0.0435(13) 0.7196(4) ? 0.038(3) 1 
O(2) 8  e  1 0.2183(8) 0.6708(3) 0.6816(3) 0.0227(14) 1 
O(3) 4  d  ..m -0.0119(10) 0.6016(4) ? 0.0195(18) 1 
O(4) 8  e  1 0.3853(8) 0.4639(3) 0.6600(4) 0.0293(16) 1 
O(5) 8  e  1 0.1881(15) 0.4311(4) 0.5578(4) 0.069(3) 1 
O(6) 8  e  1 0.0592(9) 0.4756(3) 0.6755(4) 0.0366(18) 1 
O(7) 8  e  1 0.2257(9) 0.5501(3) 0.5885(4) 0.0258(14) 1 
O(8) 8  e  1 0.1900(7) 0.7231(3) 0.4337(3) 0.0142(12) 1 
O(9) 8  e  1 0.3862(7) 0.6660(3) 0.3397(3) 0.0159(12) 1 
O(10) 8  e  1 0.0542(8) 0.6601(3) 0.3261(3) 0.0182(12) 1 
O(11) 8  e  1 0.2038(8) 0.6030(3) 0.4357(3) 0.0173(12) 1 
O(12) 8  e  1 -0.0215(8) 0.6564(3) 0.5581(3) 0.0163(12) 1 
O(13) 8  e  1 0.4452(8) 0.6641(3) 0.5502(3) 0.0183(12) 1 
O(14) 4  d  ..m 0.3061(10) 0.4482(4) ? 0.0178(17) 1 
O(15) 4  d  ..m -0.6992(11) 0.3485(4) ? 0.0170(17) 1 
O(16) 4  d  ..m -0.394(2) 0.6575(10) ? 0.132(9) 1 
Cs(1) 8  e  1 -0.28867(8) 0.54778(3) 0.60995(3) 0.02581(15) 1 
 155 
Cs(2) 8  e  1 -0.2761(1) 0.77973(5) 0.57516(6) 0.0260(4) 0.569(3) 
a Symmetry describes multiplicity, Wyckoff parameter and symmetry of the atomic site. 
b Ueq is defined as one-third of the trace of the orthogonalized Uij tensor. 
 156 
 UV-vis-NIR Diffuse Reflectance Spectra.  The diffuse reflectance spectra of 
UCoP, UNiP, and UCuP were measured from 1800 to 200 nm on a Shimadzu UV3100 
spectrophotometer equipped with an integrating sphere attachment with BaSO4 as the 
standard.  Kubelka-Monk function was used in order to transfer reflectance data to 
arbitrary absorbance units. 
 Magnetic properties. Magnetic susceptibility measurements were conducted 
using a Quantum Design superconducting interference device (SQUID), under applied 
fields ranging from 100 to 10000 gauss as a function of temperature over the range of 5 ? 
320 K and magnetization data were collected at 5 K in fields ranging from 0 ? 10,000 
gauss.  Samples were doubly encapsulated in aluminum containers, which contributed 
significantly to the measured signal, especially at higher temperatures and for samples 
with a low inherent susceptibility.  Empty containers were run independently under the 
same conditions and the data used directly for background subtraction.  Diamagnetic 
contributions to the data were also calculated and used to correct the measured 
susceptibility. 
The temperature dependent magnetic susceptibility data were analyzed assuming 
Curie-Weiss behavior with an added temperature independent term, c = C / (T-q) + cTIP, 
where C and q are Curie and Weiss constants and cTIP is the temperature-independent 
contribution to the susceptibility. C is related to the effective magnetic moment 
2/1
2
0
3
	




=
B
eff N
kC
mm in which N0 is Avogadro?s number and cB is the Bohr magneton (0.927 
x 10-20 erg/Gauss).  For cases in which cTIP is small, the effective magnetic moment can 
 157 
be obtained directly from the slope of the temperature dependence versus inverse 
magnetic susceptibility. 
Ion-exchange Studies.  NaCl, KCl, CsCl, CaCl2, and SrCl2 solutions were used 
in order to estimate ion-exchange capacities of UCoP and UCuP. Concentrations of the 
solutions of different cations were measured with classic potentiometric methods with 
ion-selective electrodes for K+, Na+, and Cs+ uptake,25 using an Accumet A15 pH meter, 
and atomic adsorption spectroscopy, using a Varian 240 AA spectrometer with hollow 
cathode Ca and Sr lamps for Ca2+ and Sr2+ uptake.   
K+-, Na+- and Cs+-selective membranes were made in according with Fluka 
recommended compositions. Silver/silver chloride electrode was used as a reference.25  In 
order to prevent contamination of tested solutions with KCl the reference electrode with 
double junction and lithium acetate as a bridging electrolyte were utilized.  
In all cases samples were equilibrated in the 5 ml capped vials with different 
cation solutions of known concentration for 48 hours at constant shaking, and then the 
change in the concentrations were determined.  The approximate volume to mass ratio 
200:1 (4 ml of the solution for 0.02 g of sample) was used in all experiments. 
Additionally the kinetic of Sr2+ uptake was studied using a 90Sr source.  10 mL of 
90Sr2+ with initial activity 20 mCu/milliliter was added to the Sr2+ solution.  One milliliter 
aliquots were taken at different time intervals, mixed with 19 mL of scintillation cocktail, 
placed in a scintillation counter and counted for 200 sec. 
 
 
 
 158 
RESULTS AND DISCUSSION  
 Syntheses.  In order to investigate new pathways to the formation of uranyl-
containing framework materials we have studied the interaction of pure transition metals  
with an acidic reaction mixture that contains uranyl nitrate, phosphoric acid, and alkali 
metal chloride under hydrothermal conditions. As Grohol and Nocera discussed for 
vanadium jarosites formation,26 slow oxidation of metallic vanadium, due to the 
passivation of the vanadium surface, can be the rate-limiting step in the formation of the 
product. We suggest that rate-limiting oxidation and therefore the dissolving step 
provides slow introduction of the transition metal to the reaction and enforces the 
formation of the multicomponent system instead of a mixture of separate metal and 
uranyl phosphates. But due to passivation of the metal surface the reaction is not 
completed and traces of metal particles can be found in the product mixture. In the same 
study the authors have searched for potential oxidants for the vanadium metal. They 
proposed that oxygen, dissolved in water, or protons could be simultaneously reduced, 
and therefore could serve as oxidants. But reaction under a nitrogen atmosphere yielded 
the same product as under oxygen atmosphere. That result revealed the oxidation nature 
of the protons.26 The oxidation potential of the Co0/Co2+, Ni0/Ni2+, and Cu0/Cu2+ are 
+0.28 V, +0.25 V and +0.15 V respectively and therefore metals can extrude the 
hydrogen from the phosphoric acid. Hence we can summarize that protons act as 
oxidizing agents in our uranyl-transition metal-phosphate formation reaction. 
 This statement has three important practical consequences. At first, we can 
conclude that the formation of all uranyl-transition metal-phosphates UCoP, UNiP, 
UCuP, UTiP, UVVP and KUVIVP (RbUVIVP) could proceed only in acidic conditions 
 159 
and an increase in pH usually led to the lower product content. In addition, according to 
suggested rate-limiting oxidation of transition metals, we could obtain near quantitative 
yield of the desired products by increasing the temperature and time of the reaction.  
Finally these general rules can be applied to most members of first-row transition metals, 
enabling uranyl-first row transition metal phosphate framework products with different 
structures and therefore with different properties to be produced in high yield.  
 Structure. Cs2{(UO2)4[Co(H2O)2]2(HPO4)(PO4)4} (UCoP) and 
Cs2{(UO2)4[Ni(H2O)2]2(HPO4)(PO4)4} (UNiP).  The structure of UCoP and UNiP 
contain three crystallographically unique uranium atoms, two of which are in pentagonal 
bipyramidal environments and one of which is in a hexagonal bipyramidal geometry. The 
fundamental building unit of UCoP and UNiP is shown in Figure 6.1.  In each case, there 
is a central uranyl core designated by two short U=O distances.  The uranyl bond 
distances are within expected limits and range from 1.767(5) to 1.800(6) ?. The uranyl 
units form longer interactions with the oxygen atoms from the phosphate anions.  These 
distances range from 2.263(5) ? to 2.507(6) ? for UCoP and from 2.308(6) ? to 
2.505(6) ? for UNiP.  The interaction of the uranyl cations and phosphate anions creates 
layers in the [ab] plane. These layers are a new topology for a uranium oxide.1,2 (Figure 
6.2) There is one crystallographically unique disordered phosphate anion present in the 
layer.  Other than the disordered unit, the phosphate units are approximately tetrahedral 
with normal P-O bond distances.  The uranyl phosphate layers are joined together by 
octahedral Co or Ni centers wherein the Co (Ni) is bound by phosphate and two cis water 
molecules.  In addition, the Co or Ni ions are also ligated by a uranyl oxo atom from the  
 
 160 
 
 
 
 
 
 
 
 
 
Figure 6.1. The fundamental building unit of UCoP includes three crystallographically 
unique U  centers, two in pentagonal bipyramidal and one in hexagonal bipyramidal 
environment, three tetrahedral P centers and Co octahedra. 50% probability thermal 
ellipsoids are represented. UNiP is isostructural with UCoP. 
 
 161 
 
 
 
 
 
 
 
 
 
 
 
Figure 6.2. View down the c axis of the uranyl phosphate layers in UCoP and UNiP. 
One of the phosphate anions is disordered and is shown in ball-and-stick format. Uranium 
polyhedra are in green and phosphate are in yellow. 
 162 
U(3) uranyl unit.  This Co-O bond distance is 2.105(5) ? and Ni-O distance is 2.065(6) 
?, and it fits well within the other Co-O or Ni-O bond distances, which range from 
2.031(5) ? to 2.159 (6) ? in UCoP and from 2.018(6) ? to 2.116(6) ? in UNiP. Bond 
distances and angles are summarized in Tables 6.5 and 6.6. This kind of interaction is 
rare,27-32 but is known from compounds such as [Cu(H2O)4](UO2HGeO4)2?2H2O.32 The 
Co and Ni centers form dimers via two 3-oxo atoms from two phosphate anions.  The 
presence of these octahedral building units stitches the structure together into a three-
dimensional framework where void spaces are filled by Cs+ cations. (Figure 6.3) There 
are channels 5.0 ? ? 5.0 ? in this structure that extend down the b axis.  The method of 
construction of this mixed metal phosphate differs from that of UGaP1, UGaP2, UTiP, 
UGeP, UVVP, KUVIVP, and RbUVIVP. Bond-valence sum calculations provide values 
of 6.08 (6.10), 6.24 (6.22), and 6.07 (6.04) for U(1), U(2), and U(3), respectively, 
confirming the expected oxidation state of +6.33  More importantly, the sum for the Co 
and Ni center is 1.98 and 1.95 respectively, consistent with that of CoII and NiII.34,35   
 Totalling the charges of the metal centers and phosphate anions reveals that there 
must be one proton within the structure.  This proton most likely resides on the terminal 
oxygen atom of the phosphate anion containing P(1).  Unfortunately, the disorder of this 
anion does not allow for conclusive bond distance comparisons. 
 Cs3+x[(UO2)3CuH4x(PO4)5]?H2O (UCuP). Similar to the structure of UCoP and 
UNiP, UCuP contains two-dimensional uranyl phosphate layers that are linked into a 
three-dimensional structure by a transition metal center.  Beyond this general similarity, 
the structures of UCoP (UNiP) and UCuP are dramatically different for a number of 
reasons.  One of these is that there are two crystallographically unique uranium centers in  
 163 
 
 
 
 
 
 
 
 
 
Figure 6.3. An illustration of the three-dimensional structure of UCoP and UNiP as 
viewed down the b axis. Uranium polyhedra are in green, phosphate in yellow, cobalt or 
nickel in orange. Purple centers represent the Cs+ cations.  
 164 
Table 6.5.  Selected Bond Distances (?) and Angles (?) for 
Cs2{(UO2)4[Co(H2O)2]2(HPO4)(PO4)4} (UCoP). 
Distances (?) 
U(1)-O(12)  1.785(6) Co(1)-O(10) 2.101(5) 
U(1)-O(11) 2.302(5) Co(1)-O(16) 2.105(5) 
U(1)-O(1) 2.333(9) Co(1)-O(14) 2.123(5) 
U(1)-O(4) 2.411(5) Co(1)-O(13) 2.159(6) 
U(2)-O(17) 1.767(5) P(1)-O(1) 1.358(9) 
U(2)-O(4) 2.405(5) P(1)-O(2) 1.602(11) 
U(2)-O(5) 2.425(5) P(1)-O(3) 1.491(7) 
U(2)-O(3) 2.459(6) P(2)-O(7) 1.497(5) 
U(3)-O(15) 1.786(5) P(2)-O(6) 1.516(5) 
U(3)-O(16) 1.794(5) P(2)-O(4) 1.557(5) 
U(3)-O(8) 2.263(5) P(2)-O(5) 1.563(5) 
U(3)-O(9) 2.302(5) P(3)-O(8) 1.521(5) 
U(3)-O(6) 2.308(5) P(3)-O(9) 1.536(5) 
U(3)-O(5) 2.391(5) P(3)-O(10) 1.555(5) 
U(3)-O(3) 2.507(6) P(3)-O(11) 1.539(5) 
Co(1)-O(7) 2.031(5) P(1)-P(1) 1.045(8) 
Co(1)-O(10) 2.099(5)   
Angles (?) 
O(12)?U(1)?O(12)  179.2(4) O(7)?Co(1)?O(14) 173.6(2) 
O(17)?U(2)?O(17) 179.2(3) O(10)?Co(1)?O(13) 177.0(2) 
O(15)?U(3)?O(16) 178.1(2) O(10)?Co(1)?O(16) 174.5(2) 
 165 
Table 6.6.  Selected Bond Distances (?) and Angles (?) for 
Cs2{(UO2)4[Ni(H2O)2]2(HPO4)(PO4)4} (UNiP). 
Distances (?) 
U(1)-O(12)  1.780(7) Ni(1)-O(10) 2.067(6) 
U(1)-O(11) 2.308(6) Ni(1)-O(16) 2.065(6) 
U(1)-O(1) 2.331(11) Ni(1)-O(14) 2.083(6) 
U(1)-O(4) 2.410(5) Ni(1)-O(13) 2.116(6) 
U(2)-O(17) 1.774(6) P(1)-O(1) 1.352(11) 
U(2)-O(4) 2.401(6) P(1)-O(2) 1.661(15) 
U(2)-O(5) 2.420(6) P(1)-O(3) 1.504(8) 
U(2)-O(3) 2.449(6) P(2)-O(7) 1.501(6) 
U(3)-O(15) 1.783(6) P(2)-O(6) 1.509(6) 
U(3)-O(16) 1.800(6) P(2)-O(4) 1.562(6) 
U(3)-O(8) 2.261(6) P(2)-O(5) 1.562(6) 
U(3)-O(9) 2.312(6) P(3)-O(8) 1.521(6) 
U(3)-O(6) 2.311(6) P(3)-O(9) 1.544(6) 
U(3)-O(5) 2.396(5) P(3)-O(10) 1.548(6) 
U(3)-O(3) 2.505(6) P(3)-O(11) 1.538(6) 
Ni(1)-O(10) 2.074(6) P(1)-P(1) 1.061(9) 
Ni(1)-O(7) 2.018(6)   
Angles (?) 
O(12)?U(1)?O(12)  179.6(5) O(7)?Co(1)?O(14) 174.2(2) 
O(17)?U(2)?O(17) 179.9(4) O(10)?Co(1)?O(13) 177.8(2) 
O(15)?U(3)?O(16) 177.4(3) O(10)?Co(1)?O(16) 175.6(2) 
 166 
UCuP that are found as UO6 tetragonal bipyramids and UO7 pentagonal bipyramids. 
(Figure 6.4) The uranyl U=O bond distances for these two polyhedra range from 1.770(6) 
? to 1.803(8) ?.  
 The equatorial U-O distances range from 2.236(5) ? to 2.514(5) ?. Selected bond 
distances and angles for UCuP are given in Table 6.7. Taking into account the 
differences in coordination number, these distances were used to calculate bond-valence 
sums of 5.96 and 6.08 for U(1) and U(2), respectively.33  The uranyl moieties are bridged 
by phosphate anions into sinusoidal sheets that extend into the [bc] plane. (Figure 6.5)  
Again, this is apparently a new layered topology for a uranium oxide compound.1,2  The 
uranyl phosphate layers in UCuP are interconnected by Cu centers that reside in square 
planar environments, being bound by four phosphate anions with two Cu-O distances of 
1.962(6) ? and 1.964(6) ?.  The bond-valence sum for the Cu site is 1.85 and is 
consistent with that of CuII.34,35   
 The overall structure is three-dimensional.  However, the structure is much less 
open than that of UCoP and UNiP or other mixed-metal uranyl transition metal 
phosphates prepared thus far.  Channels for the Cs+ cations and water molecules that are 
observed in other mixed-metal uranyl phosphate structures are not as distinct in UCuP, 
although there are found channels 3.2 ? ? 4.1 ? extending down the c axis. (Figure 6.6)  
Of interest, however, is that there are two Cs+ sites within the channels.  One of these 
sites is fully occupied.  The second site is occupied by 0.57.  This has important 
consequences for the degree of protonation for UCuP.  There are two phosphate anions 
with terminal oxo atoms in the structure.  For the phosphate anion containing P(1), there 
  
 167 
 
 
 
 
 
 
 
 
 
 
 
Figure 6.4. A view of the uranyl tetragonal and pentagonal bipyramids, square planar Cu 
and phosphate tetrahedra in UCuP with 50% probability ellipsoids.   
 168 
Table 6.7.  Selected Bond Distances (?) and Angles (?) for 
Cs3+x[(UO2)3CuH4x(PO4)5]?H2O (UCuP). 
Distances (?) 
U(1)-O(15)  1.782(8) Cu(1)-O(6) 1.964(6) 
U(1)-O(14) 1.803(8) P(1)-O(2) 1.501(6) 
U(1)-O(9) 2.236(5) P(1)-O(1) 1.560(9) 
U(1)-O(4) 2.254(6) P(1)-O(3) 1.560(8) 
U(2)-O(12) 1.770(6) P(2)-O(4) 1.509(6) 
U(2)-O(13) 1.777(6) P(2)-O(6) 1.509(7) 
U(2)-O(7) 2.263(6) P(2)-O(7) 1.509(7) 
U(2)-O(2) 2.310(6) P(2)-O(5) 1.548(7) 
U(2)-O(8) 2.369(5) P(3)-O(10) 1.525(6) 
U(2)-O(11) 2.399(5) P(3)-O(11) 1.531(6) 
U(2)-O(8) 2.514(5) P(3)-O(9) 1.543(6) 
Cu(1)-O(10) 1.962(6) P(3)-O(8) 1.557(6) 
Angles (?) 
O(15)?U(1)?O(14)  179.4(3) O(10)?Cu(1)?O(6) 178.7(3) 
O(9)?U(2)?O(4) 178.4(2) O(6)?Cu(1)?O(6) 86.0(5) 
O(10)?Cu(1)?O(10) 88.4(3)   
 
 
 
 
 
 169 
 
 
 
 
 
 
 
Figure 6.5. Depiction of uranyl phosphate layers in UCuP. Uranyl polyhedra are in green 
and phosphates are in yellow.  
 170 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 6.6. View of the three-dimensional structure of UCuP wherein the CuII centers 
link uranyl phosphate layers together. Uranium polyhedra are in green, phosphate in 
yellow, and copper in blue. Some of the Cs+ sites have been omitted for clarity. 
 171 
are two terminal oxo atoms with P-O bond distances of 1.560(9) ?, as compared to the 
bridging P-O bond distances of 1.501(6) ?.  We propose that both of these 
aforementioned sites are protonated.  A second phosphate anion containing P(2) has three 
bridging P-O bond distances of 1.509(7) ? and one terminal distance of 1.548(7) ?.  This 
latter site is likely to be protonated also.  However, if all three of these terminal sites are 
fully protonated, then there is an excess positive charge of 0.14.  A closer look at the 
terminal oxygen atom around P(2) reveals an elongated thermal ellipsoid for this atom.  
We speculate that this elongation represents an average of protonated and deprotonated 
oxygen positions.  Therefore, a potentially correct formula for UCuP can be written as 
Cs3.14[(UO2)3Cu(H2PO4)(H1.93PO4)2(PO4)2]?H2O.  
 UV-vis-NIR diffuse reflectance study. Spectroscopic verification of the 
oxidation state for Co, Ni and Cu was provided by UV-vis-NIR diffuse reflectance 
spectroscopy.  In the case of UCoP (Figure 6.8) the spectrum yields three main bands 
that are expected for octahedral CoII.36  4T2g---4T1g transition is located at 9700 cm-1 (1030 
nm).  The band at 19100 cm-1 (525 nm) matches with 4T1g(P)---4T1g, that is usually seen 
in the visible region.  Additionally, a very weak band located around 13000 cm-1 (770 
nm), corresponds to an 4A2g transition, which usually appears as a shoulder.  
 The spectrum of UNiP (Figure 6.9) reveals three main bands at 10100 cm-1 (990 
nm), 16700 cm-1 (600 nm) and 21200 cm-1 (470 nm), that correspond to spin allowed 
transitions from 3A2g to 3T2g, 3T1g 3T1g(P) respectively.  Also two weak features of spin 
forbidden transitions to 1Eg and 1T2g at 14100 cm-1 (710 nm) and 18000 cm-1 (560 nm) 
might be seen at the spectra.  These data are consistent with octahedral NiII.36  
  
 172 
 
 
 
0
10
20
30
40
50
60
0 10000 20000 30000 40000 50000
Wavenumber, cm-1
F
(
R
)
9700
13000
19100
25100
 
 
 
 
 
 
 
Figure 6.7. UV-vis-NIR diffuse reflectance spectrum of UCoP. F(R) corresponds to 
Kubelka-Monk function and relates reflectance data to the absorption spectra.37   
 173 
 
 
 
 
0
10
20
30
40
50
60
0 10000 20000 30000 40000 50000
Wavenumber, cm-1
F
(
R
)
10100
14100
16700 18000
21200
25600
 
 
 
 
 
 
 
Figure 6. 8. UV-vis-NIR diffuse reflectance spectrum of UNiP. F(R) corresponds to 
Kubelka-Monk function and relates reflectance data to the absorption spectra.37   
 174 
There is a broad band with a maximum at 17800 cm-1 (560 nm) in the spectra of UCuP 
corresponding to the d-d z2 to x2 - y2 transition expected for square planar CuII.36 (Figure 
6.9) 
In addition in all spectra, absorption features centered between 25100 cm-1 ? 
26000 cm-1 (380 ? 400 nm) are present with considerable fine structure.  These features 
are assigned to absorption by the uranyl cation.38,39  
 Magnetization Measurements. The magnetic susceptibility of UCoP was 
measured as a function of temperature under a constant field of 2000 G.  Such a large 
field was necessary to assure adequate counting statistics at higher temperature.  Even at 
such a high field, only about 40% of the measured signal arises from the sample at higher 
temperatures.  The linearity of the susceptibility of UCoP was verified by independent 
measurements of the magnetization at 5 K as a function of field at fields up to 2000 G. 
(Figure 6.10)  The temperature dependence of the magnetic susceptibility of UCoP, along 
with its inverse, is shown in Figure 6.11.  From the temperature dependence, there is no 
indication of any magnetic ordering down to 5 K, the lowest temperature measured.  The 
absence of significant ferromagnetic or spin-glass behavior is supported by a comparison 
of field-cooled and zero-field-cooled data, which showed no significant differences.  The 
effective magnetic moment, per mole of UCoP sample, was determined to be 4.95(10) B 
from the fit to the Curie-Weiss law, and measured TIP and  are -0.00012(2) emu/mole 
Co and 0.3(5) K, respectively.  The effective magnetic moment obtained from the 
temperature dependence of inverse magnetic susceptibility between 100 and 300K is 
4.99(5), which is consistent with moments observed in other  
 
 175 
 
 
 
 
0
5
10
15
20
25
30
35
40
45
10000 15000 20000 25000 30000 35000 40000 45000 50000
Wavenumber, cm-1
F
(
R
)
17200
26000
 
 
 
 
 
 
 
 
Figure 6.9. UV-vis-NIR diffuse reflectance spectrum for UCuP. F(R) corresponds to 
Kubelka-Monk function and relates reflectance data to the absorption spectra.37   
 176 
 
 
 
 
 
 
 
 
Figure 6.10. Magnetization of UCoP as a function of applied magnetic field at 5 K.  Line 
is the linear fit to the data. 
 177 
 
 
 
 
Figure 6.11. Magnetic susceptibility of UCoP as a function of temperature.  Line is the 
fit to Curie-Weiss behavior.  Inset shows the temperature dependence of the inverse 
magnetic susceptibility with a linear fit.  
 178 
systems with octahedrally coordinated Co2+ ion.  The TIP is small and is consistent with 
isolated Co2+ spins, as is the Weiss constant. 
The magnetization and the temperature dependence of the magnetic susceptibility 
of UCuP (Figure 6.12 and 6.13) show no evidence of magnetic ordering.  Both field 
cooled and zero field cooled magnetic susceptibilities of UCuP were measured and are 
statistically indistinguishable, adding support to the absence of magnetic ordering seen 
from the temperature dependence.  The effective magnetic moment for Cu2+ ion in this 
compound was determined to be 1.9(1) B from the fit to the Curie-Weiss law, and 
measured TIP and  are 0.0004(1) emu/mole Co and -0.3(5) K, respectively.  The 
effective magnetic moment obtained is consistent with moments observed in other 
systems with Cu2+ ions.  
 Thermal analysis. In order to estimate the thermal stability of samples we have 
collected DSC data for UCoP and UCuP compounds.  Both structural types demonstrate 
complicated thermal behavior.  Lost of surface water of UCoP at 155 ?C is followed by a 
series of the endothermic events corresponding to the structural rearrangements, 
beginning at 273 ?C. (Figure 6.14) Two major events at 400 ?C and 414 ?C could be 
assigned to the loss of two crystallographically distinct water molecules bonded to the Co 
center.  UCuP consequently loses surface and interstitial water at 130 ?C and 160 ?C. 
(Figure 6.15) The series of peaks, exothermic - at 290 ?C and endothermic ? at the 
temperature above 400 ?C, clearly indicate decomposition of the structure and lost of 
crystallinity at high temperatures.    
 
 
 179 
 
 
 
 
 
 
 
Figure 6.12. Magnetization of UCuP as a function of applied magnetic field at 5 K.  Line 
is the linear fit to the data. 
 180 
 
 
 
 
Figure 6.13. Magnetic susceptibility of UCuP as a function of temperature.  Line is the 
fit to Curie-Weiss behavior.  Inset shows the temperature dependence of the inverse 
magnetic susceptibility.  
 181 
  
 
 
 
-1.6
-1.1
-0.6
-0.1
0.4
0.9
0 100 200 300 400 500 600
Temperature, oC
H
e
a
t
 
f
l
o
w
,
 
m
W
.
 
.
155oC 273oC
400oC 414oC
592oC536
oC
 
 
 
 
 
 
 
 
 
 
Figure 6.14. DSC data for UCoP.  
 182 
 
 
 
-0.4
-0.35
-0.3
-0.25
-0.2
-0.15
-0.1
-0.05
0
0 100 200 300 400 500 600
Temperature, oC
H
e
a
t
 
f
l
o
w
,
 
m
w
.
 
.
130oC
160oC
290oC
400oC
510oC
540oC
 
 
 
 
 
 
 
 
 
Figure 6.15. DSC data for UCuP.  
 183 
 Ion exchange properties. The difference in the structures of UCoP and UCuP 
leads to their different ion-exchange capabilities.  The highest uptake from 1?10-2 M 
solutions of UCoP demonstrates toward Na+ cations.  The value is 0.6(1) meq/g that 
roughly corresponds to one half of the theoretical capacity and is consistent with the 
exchange of one out of two Cs+ cations that occupy the channels.  The pH of the solutions 
is not changed significantly during the exchange experiments that suggests protons do not 
participate in the exchange. The equilibration of the UCoP with CsCl solutions has also 
revealed no change of pH and Cs+ concentration, which implies that there are no 
exchangeable protons in the structure.  The capability toward Sr2+ and Ca2+ is smaller 
(0.28(6) meq/g and 0.20(8) meq/g, respectively).  Assuming that 2 moles of Cs+ are 
necessary for exchange with 1 mol of Sr2+ or Ca2+, Sr2+ exchange corresponds only to one 
quarter of the calculated capacity.  These results are significantly higher than Sr2+ uptake 
0.1(2) meq/g, measured by radiotracer method.  The measurements of radioactivity of Sr 
solution, containing 90Sr isotope, after different time intervals of exchange, allow one to 
assume that 80% of exchange occurs within first 10 minutes after mixing.  The lower 
uptake values can be explained by the much higher volume to mass ratio, exceeding 
3000:1.   
 In the mixed solutions Ca2+/Na+, Sr2+/Na+ and Ca2+/Sr2+, the uptake of alkaline 
earth cations by UCoP is highly preferable with no exchange of Na+ occurring.  This 
selectivity can result from the relatively large size of the channels (5.0 ? ? 5.0 ?).  Those 
channels are large enough to accommodate even hydrated cations, and radii of Ca2+ (4.1 
?) and Sr2+ (3.9 ?)40 in their hydrated shells fit better than smaller Na+ (3.6 ?).40  Finally, 
 184 
there is no selectivity found between Sr2+ and Ca2+. They are taken from the mixed 
solutions in a 1:1 ratio.  
 UCuP ion-exchange experiments showed strong ion-exchange capacities toward 
double-charged cations with uptake values of 0.49 meq/g and 0.51 meq/g for Ca2+ and 
Sr2+ respectively and no exchange for Na+ and K+.  Again no selectivity between Ca2+ and 
Sr2+ is found in the mixed solutions.  During the experiments it was noted that the pH of 
the solutions at ion-exchange equilibrium drops by approximately 3 units in all solutions.  
This might be explained either as participation of the structural protons that belong to the 
phosphoric acid in the exchange or presence of the excess of phosphoric acid on the 
surface of material.  But due to the very similar change of pH, ranging within 0.4 units 
for all solutions and no notable dependence of this change from the concentration of 
present cation, we can rather accept that pH of the solutions is defined by the amount of 
phosphoric acid remaining on the surface after the synthesis.  
 
CONCLUSION  
 The combination of the work reported herein along with our previous disclosures 
on Cs4[(UO2)2(GaOH)2(PO4)4]?H2O,9 Cs[UO2Ga(PO4)2],9 Cs1.52[(UO2)(TiOH0.48)(PO4)2] 
?nH2O, Cs1.35[(UO2)(GeOH0.65)(PO4)2]?nH2O, Cs2[(UO2(VO2)2(PO4)2]?nH2O10 and 
K4(UO2)(VO)4(OH)2(PO4)4 (Rb4(UO2)(VO)4(OH)2(PO4)4) demonstrates that the 
construction of mixed-metal uranyl phosphates with three-dimensional framework 
structures can be accomplished by the interconnection of one-dimensional uranyl 
phosphate and main group or transition metal phosphate substructures, the linking of 
uranyl phosphate layers by transition metal centers, or linking of metal-phosphate layers 
 185 
by uranyl centers.  The main group or metal centers contained in these structures span 
from tetrahedral environments in UGaP2 to square planar geometries in UCuP, to square 
pyramidal coordination in UVVP to octahedral UGaP1, KUVIVP, RbUVIVP, UCoP, and 
UNiP.  Likewise, the UO6 tetragonal bipyramid, the UO7 pentagonal bipyramid, and the 
UO8 hexagonal bipyramid all occur in this small group of compounds, illustrating the 
remarkable structural diversity of UVI.  It is now clear that the incorporation of additional 
metal centers into uranyl phosphates provides for substantial enhancement in their ion- 
exchange, nonlinear optical, and magnetic properties.  
 186 
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 189 
CHAPTER 7 
SUMMARY 
 This chapter is a summary of data and discussions reported in the dissertation, as 
well as general conclusions. 
 All reported compounds are crystalline solids synthesized under hydrothermal 
conditions at the temperatures between 180 ?C and 220 ?C.  The structures were 
determined using single crystal X-ray diffraction.  Spectroscopic data, second-harmonic 
generation of light,  thermal analysis, magnetic susceptibility, and ion-exchange were 
employed in order to characterize these materials.  
 Chapter 2 describes the structure and ion-exchange properties of the potassium 
uranyl iodate, K[UO2(IO3)3] (KUI).  This compound was prepared as a continuation of 
the search for novel uranyl iodates, conducted in our group.  KUI has a structure 
consisting of layers of uranyl iodate with potassium cations located between the layers. 
The K+ can be exchanged with Cs+ with uptake value of 1.7 meq/g.  
 Two novel uranyl gallium phosphates, Cs4[(UO2)2(GaOH)2(PO4)4]?H2O (UGaP1) 
and Cs[UO2Ga(PO4)2] (UGaP2) with open-framework structures are discussed in 
Chapter 3.   These two compounds are the first result of our program for preparing uranyl 
compounds with three-dimensional open-framework structures with a particular focus on 
the use of octahedral centers, as building units.   We suggested that incorporation of the 
octahedral building blocks in the structure, where bond formation is allowed in axial and 
 190 
equatorial planes, will aid in the formation of frameworks.  The three-dimensional 
structure of UGaP1 is constructed in accordance with this hypothesis from uranyl 
pentagonal bipyramids, phosphate tetrahedra, and gallium octahedra.  The UGaP2 open-
framework structure contains uranyl pentagonal bipyramids, phosphate and gallium 
tetrahedra, and no octahedral building blocks.  
 Both UGaP1 and UGaP2 structures have channels filled with Cs+ cations.   Ion-
exchange experiments show the ability of the Cs+ cations in UGaP1 to be exchanged 
with divalent Ca2+, Sr2+, and Ba2+, in UGaP2 - with Ca2+and Ba2+.   We were focused on 
the measurements of Sr2+ uptake in the presence of Na+ due to the potential application of 
the ion-exchange materials for the removal of 90Sr2+ from HLNW.  The Sr2+ uptake in the 
presence of Na+ cations is 0.4 meq/g.   The thermal analysis revealed the absence of any 
structural changes of UGaP1 up to 400 ?C.  These data indicate that UGaP1 could be a 
potential 90Sr selective material and should be studied further.  
 In Chapter 4,5, and 6 we have proposed a new synthetic approach of utilizing pure 
element powders as starting materials for hydrothermal synthesis.  UVVP, KUVIVP 
(RbUVIVP), UTiP, UGeP, UCoP, UNiP, and UCuP are obtained using this method.   
The presence of protons from phosphoric acid and oxygen in reaction vessel allow for 
slow oxidation of transition metals or germanium and rate-limiting delivery of oxidized 
reactant to the reaction mixture.  
 In Chapter 4 we reported three novel open-framework uranyl vanadium 
phosphates Cs2[UO2(VO2)2(PO4)2]?nH2O (UVVP), and isostructural 
K4(UO2)(VO)4(OH)2(PO4)4 (KUVIVP) and Rb4(UO2)(VO)4(OH)2(PO4)4 (RbUVIVP).  
The structure of UVVP is built of tetragonal bipyramidal uranium, tetrahedral phosphate, 
 191 
and square pyramidal vanadium building units.  The terminal oxo atoms of vanadyl are 
aligned in one direction, causing the polarity of UVVP (space group Cmc21) and, as 
result, non-linear optical properties.  
 KUVIVP and RbUVIVP are constructed from uranyl tetragonal bipyramids, 
tetrahedral phosphate and vanadyl octahedral building blocks.  K+ or Rb+ cations are 
located in the channels and can be exchanged by Cs+ in the presence of Na+.  Again, this 
material can be proposed for removal of 137Cs+ from nuclear waste.  KUVIVP and 
RbUVIVP also demonstrate paramagnetic behavior at the temperatures between 100 K 
and 320 K and antiferromagnetic ordering at 52 K.  
 The isostructural compounds Cs1.52[(UO2)(TiOH0.48)(PO4)2]?nH2O (UTiP) and 
Cs1.35[(UO2)(GeOH0.65)(PO4)2]?nH2O (UGeP) are described in Chapter 5.  The open-
framework structures of these compounds include Ti or Ge in octahedral coordination 
environments.  Ti and Ge octahedra form corner-sharing chains along the same direction 
as the terminal uranyl oxygen atoms are aligned, providing for the formation of three-
dimensional structures.  
 In Chapter 6 we present the structures and properties of 
Cs2{(UO2)4[Co(H2O)2]2(HPO4)(PO4)4} (UCoP),  Cs2{(UO2)4[Ni(H2O)2]2(HPO4)(PO4)4} 
(UNiP), isostructural with UCoP,  and  Cs3+x[(UO2)3-xCuH4-x(PO4)5]?H2O (UCuP).  Co 
and Ni in octahedral coordination environment are utilized in order to build UCoP and 
UNiP open-framework structures.  Cu is incorporated in the three-dimensional structure 
of UCuP in square planar environments.  All three open-framework structures have 
channels, occupied by Cs+ cations. Cs+ can be replaced by Sr2+ in the presence of Na+ 
with uptake values 0.28 meq/g for UCoP and 0.51 meq/g for UCuP.  
 192 
 Thus, we can summarize that ten uranyl-containing open-framework and one 
layered material have been produced.  The novel strategy of incorporation of octahedral 
building units in order to synthesize open-framework structures was successful. UGaP1, 
KUVIVP, RbUVIVP, UCoP, and UNiP are constructed in accordance with this strategy. 
Two of the materials (KUI and KUVIVP (RbUVIVP)) possess ion-exchange properties, 
selective for Cs+. Cations in four materials (UGaP1, UCoP, UNiP, and UCuP) can be 
selectivity exchanged with Sr2+.  These properties make KUI, KUVIVP (RbUVIVP), 
UGaP1, UCoP, UNiP, and UCuP promising materials for the selective removal of 137Cs+ 
and 90Sr2+ from the highly radioactive nuclear waste.  Thermally stable UGaP1 could be 
recommended for the further investigations under the conditions simulating HLNW.