University of Charleston, USA
Posters & Accepted Abstracts: Mod Chem appl
The linear uranyl UO2 2+(VI) cation (D�??h symmetry) exhibited strong charge-transfer absorptions at 350-400 nm in the media containing reductive bromide (Br-), iodide (I-), methanol (CH3OH), ethanol (CH3CH2OH), phenol (PhOH), DMSO (CH3SOCH3), diphenyl sulfide (Ph2S), and diphenyl selenide (Ph2Se). The absorptions originate from a single-electron transfer from the reductant to the uranium (VI) valence shell. Their intensities (absorbances at 375 nm) have been found to be directly proportional to molar concentrations of the reductant and UO2 2++ in solution, respectively, showing the nature of a bimolecular interaction in the charge-transfer transition. Electron Paramagnetic Resonance (EPR) studies have shown that the charge-transfer (single-electron transfer) also took place slowly in the dark, resulting in thermal reduction of UO2 2++ (VI) to UO2+ (V) (g=2.08) by each of the reductants. The reductants were oxidized to stable radicals. For example, bromide in the aqueous medium was oxidized by UO2 2++ to a stable bromide-bromine anion-radical pair Br2 -. (g=1.92). RCH2OH (R=H or CH3) was oxidized by UO2 2++ to the α-hydroxylalkyl R.CHOH radical, which likely forms a cation-radical pair with U(V) (UO2 +, R.CHOH) stabilizing the radical. In acetone, Ph2Se was oxidized by UO2 2++ to the Ph2Se. (g=2.00) radical likely forming a stable cation-radical pair with uranyl (V) (UO2 +, Ph2Se.). In the presence of sulfuric acid, CH3SOCH3 (DMSO) was shown to undergo a charge-transfer oxidation by UO2 2++(VI) to a stable CH3SOCH2. (DMSO.) Radical (g=2.01), and UO2 2++(VI) was reduced to UO2 +(V). A thermal oxidation-reduction of UO2 2++ (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.