RAMAN, RESONANCE RAMAN AND INFRARED-SPECTRA OF POTASSIUM URANYL CROCONATE

The Raman, resonance Raman and IR spectra of potassium uranyl croconate, UO2(H2O)K2(C5O5)2 were obtained and interpreted. Several croconate modes are split indicating a substantial decrease in the oxocarbon symmetry, as is to be expected from a recent crystallographic investigation, revealing the coordination of the oxocarbon to be two non-equivalent UO22+ moieties in a monodentate fashion. In terms of vibrational frequency shifts it can be concluded that the UO22+ moiety behaves as an isolated oscillator. The resonance Raman results suggest that the strong band centered around 450 nm in the UV-vis spectrum should be assigned to a charge transfer transition from the oxocarbon to the uranyl ion. In fact, as resonance is approached, both uranyl and croconate modes are enhanced. It can also be inferred that the chromophore is rather delocalized into the oxocarbon ring, rather than localized in the carbonyl groups as previously observed for other croconate complexes.