Synthesis and Characterization of Tetra- and Penta-dentate Schiff Base Complexes for Application in Actinide Sensing
Type of DegreePhD Dissertation
Chemistry and Biochemistry
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The advent of the nuclear power era has the potential to provide inexpensive, plentiful electricity with reduced carbon emissions, but these benefits are offset by concerns about the potential environmental effects of a waste spill or contamination event. Further exploration into the fundamental actinide and lanthanide coordination chemistry could provide knowledge that can be applied to nuclear waste detection and remediation. A fruitful method that has been employed to sequester and identify actinides, especially in selective sequestration even in the presence of lanthanides, has been to incorporate softer nitrogen donor atoms and pair them with phenolate donors. Here, the systematic characterization by X-ray crystallography and UV-visible spectroscopy of a salphenazine ligand (H 2 L I ), containing the O-N-N-O salen type bonding motif, and corresponding metal complexes revealed the extended π-conjugation of these ligands results in differentiation of a uranyl signal as compared to these transition metal contaminants. A series of new pentadentate binding ligands (H 2 L III -H 2 L VI ), which fully occupy the uranyl equatorial plane, removed the necessity of a coordinating solvent molecule or ligand rearrangement allowing to quickly and selectively bind uranyl in a one to one fashion. To further explore the f- element coordination chemistry with salen-type ligands, eleven lanthanide double decker sandwich complexes (Ln 2 [L VII ] 3 ) were synthesized and characterized and found to posses tunable solution and solid-state emission properties, with Sm 2 [L VII ] 3 emission at 556 nm to Er 2 [L VII ] 3 emission at 617 nm. Interestingly, lutetium exhibited a significant increase in fluorescent signal as compared to the other Ln 2 [L VII ] 3 complexes in the solid state, providing a rare opportunity to 3 differentiate one of the 14 lanthanides. Lastly, the double-decker thorium and cerium sandwich complexes, of the type M[L VII ] 2 were synthesized; the thorium analogue was observed to possess unprecedented emission characteristics, and is the first example of this behavior reported in the literature. These observations about the preferential binding of uranyl and unexpected electronic properties from thorium provide insights into the fundamental coordination chemistry of the early actinides and may be useful for the future design of selective ligands for actinide and lanthanide detection and separations.