The uranyl UO22+(VI) cation exhibited strong charge-transfer absorptions at 350-400 nm in the aqueous solutions containing bromide and iodide. The charge-transfer absorptions originate from a single-electron transfer from a halide anion to the uranium(VI) valence shell. Their intensities (absorbances at 375 nm) have been found to be directly proportional to molar concentrations of the halide (bromide or iodide) and UO22+ in solution, respectively, showing the nature of a bimolecular interaction in the charge-transfer transition. The absorptions were also greatly enhanced by acid. An EPR study has indicated that the charge-transfer also took place slowly in the dark, resulting in appreciable chemical reduction of UO22+(VI) to UO2+(V) (g=2.08) by bromide and iodide. In addition, a stable bromide-bromine anion-radical pair Br2-. (quartet, g=1.92, a=85G) was identified. In the presence of sulfuric acid, CH3SOCH3 (DMSO) was shown by EPR to undergo a charge-transfer oxidation by UO22+(VI) to a stable CH3SOCH2. (DMSO.) radical (g=2.01), and UO22+(VI) was reduced to UO2+(V). A chemical oxidation-reduction of UO22+(VI) and phenol in acetone was found by EPR to give UO2+(V) and a stable phenoxyl (PhO.) radical (g=2.00) via a charge-transfer pathway.

Investigation on charge-transfer absorptions of uranyl UO22+(VI) and chemical reduction of UO22+(VI) to UO2+(V) by UV-visible and EPR spectroscopies

249th National Meeting (2015)

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