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) Å to 4.287(4) Å. These interactions were probed using luminescence and Raman spectroscopy which displayed little effect on the luminescence intensity and the energy of the Raman active UO 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.