Emission Properties of Coordination Complexes: The Impact of Mixed Donors on f-Block Elements

Abstract

There is a growing need to understand the fundamental aspects of chemistry concerning f-elements. Whether it be through the use of softer donor systems to try and selectively coordinate actinide ions in solution which could be useful in the event of a spill or contamination event, using mixed donor systems to take advantage of the distinct photophysical properties of Ln (III) ions for new emissions agents for biological imaging compounds. The 4f or 5f orbitals play a pivotal role in their unique chemistry, emission, and optical properties, accessible to these elements. Here, we look at three different aspects of f-element chemistry that allow us to look at the nature of the f-orbitals while looking at how this affects their emissive properties.

The highly conjugated salimidizine ligand and 3 derivatives are examined for the electronic properties of the ligand and how these can be altered both for selective coordination of metal ions and somewhat tunable emissions. These properties would enable it to be potentially be used in colorimetric or fluorescence sensors for uranyl detection in solution. Examination of these organic frameworks is examined in the presence of copper (II) ions which are considered to be a common “false positive” metal ion due to similar charge to ionic size ratios. Overall, these organic frameworks are able to distinguish via fluorescence intensity the binding of uranyl versus copper. Further details and explanation for this is given through computational modeling of the complexes.

Next, the ability of cyano substituted naphthylsalophens were examined as sensitizers or antennae with Ln (III) ions for 2 photon up-conversion processes. This Schiff base type (-2) ligand forms 3:2 ligand to lanthanide sandwich-type complexes that display characteristic metal centered emission for Nd (III), Er (III), and Yb (III). Upon excitation at 980 nm, in mixed lanthanide complexes and Er (III) complexes, Er-centered up-conversion emission is observed at 543 nm and 656 nm respectively. This is achieved with power densities as low as 2.18 W cm-2.

Lastly, the naphthylpyrasal ligand in metal complexes was examined. These complexes were characterized through UV-vis spectroscopy, electrochemical analysis, and single crystal X-ray diffraction. This framework shows the ability in solid state to form N-oxide species in the solid state which is not commonly seen with actinides. Three distinct crystallographic species are formed showing a solvent dependance on crystallization solvent mixtures to produce different solid-state morphologies. This species seems to be formed through the presence of peroxides in the crystallization solvents. Through further examination of the solid state, we see that two of these structures produce close to a 5° bend from linearity in the typically linear -yl oxygen bonds.