VIBRATIONAL AND LOW-TEMPERATURE OPTICAL-SPECTRA OF THE URANYL TRICARBONATO COMPLEX [UO2(CO3)3]4-

Diffuse reflectance (20,000-30,000 cm-1) and luminescence (18,000-21,000 cm-1) spectra of polycrystalline Na4[UO2(CO3)3] have been measured in the temperature range of 4.2-300 K; the i.r. (50-2000 cm-1) and Raman (50-2000 cm-1) spectra have been recorded at room temperature. The vibrational spectra exhibit all frequencies expected for a UO2L3 complex of D3h symmetry with bidentate ligands L. The symmetric and asymmetric stretching vibrations of the uranyl ion occur at wave numbers as low as 808 and 843 cm-1, respectively, indicating strong uranium ← carbonate bonding. The diffuse reflectance spectra consist of four overlapping electronic transitions, the lowest one with origin at 20,680 cm-1 is also seen in emission. The absorption bands are assigned to the spin and parity forbidden components of the πu→δu and πu→φu one-electron excitations. From the splitting of the excited configurations π3uδ1u and π3uφ1u the spin-orbit coupling constant is calculated to be ζ5f{hook} = 1750 cm-1. Possible relationships between measurable spectroscopic properties of the uranyl ion and the strength of bonding in the equatorial plane are discussed. © 1979.