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

The Raman, resonance Raman and IR spectra of potassium uranyl croconat e, UO2(H2O)K2(C5O5)2 were obtained and interpreted. Several croconate modes are split indicating a substantial decrease in the oxocarbon sym metry, as is to be expected from a recent crystallographic investigati on, revealing the coordination of the oxocarbon to be two non-equivale nt UO22+ moieties in a monodentate fashion. In terms of vibrational fr equency shifts it can be concluded that the UO22+ moiety behaves as an isolated oscillator. The resonance Raman results suggest that the str ong band centered around 450 nm in the UV-vis spectrum should be assig ned to a charge transfer transition from the oxocarbon to the uranyl i on. In fact, as resonance is approached, both uranyl and croconate mod es are enhanced. It can also be inferred that the chromophore is rathe r delocalized into the oxocarbon ring, rather than localized in the ca rbonyl groups as previously observed for other croconate complexes.