A spectroscopic, structural, and computational study of Ag-oxo interactions in Ag+/UO22+ complexes

Twelve novel Ag+/UO22+ heterometallic complexes have been prepared and characterized via structural, spectroscopic, and computational methods to probe the effects of Ag-oxo interactions on bonding and photophysical properties of the uranyl cation. Structural characterization reveals Ag-oxo interaction distances ranging from 2.475(3) A to 4.287(4) A. These interactions were probed using luminescence and Raman spectroscopy which displayed little effect on the luminescence intensity and the energy of the Raman active UvO symmetric stretch peak as compared to previously reported Pb-oxo interactions. Computational efforts via density functional theory-based natural bond orbital analysis revealed that the highest stabilization energy associated with the Ag-oxo interaction had a value of only 11.03 kcal mol(-1) and that all other energy values fell at 7.05 kcal mol(-1) or below indicating weaker interactions relative to those previously reported for Pb2+/UO22+ heterometallic compounds. In contrast, quantum theory of atoms in molecules analysis of bond critical point electron density values indicated higher electron density in Ag-oxo interactions as compared to Pb-oxo interactions which suggests more covalent character with the Ag+. Overall, this data indicates that Ag+ has a less significant effect on UO22+ bonding and photophysical properties as compared to other Pb2+, likely due to the high polarizability of the cation.