EPR Study of ￥?(1,2)-[HnSiV￥3VW10O40](7-n)- (n = 0, 1 or 2). Identification of Four One-Electron Reduction Products and Evidence for Proton Transfer in the Solid State

摘要

Several one-electron reduction products of ャ (1,2)-[HnSiV2W10O40](6-n)- were separated by precipitating or coprecipitating with diamagnetic host compounds at different pH. Mono-and diprotonated species, 1 and 2, in powder samples exhibit aPR spectra characteristic of a mononuclear oxovanadium species, indicating that the unpaired electron is trapped at one vanadium atom. The EPR spectrum of the unprotonated species 0 shows 15 parallel lines, indicating that the unpaired electron interacts equally with two vanadium atoms. While different species were precipitated depending upon the pH of the solution and the charge of the host anion, only one species 1` was formed in the frozen solutions at pH 3.2-4.7. The EPR spectrum of 1` indicates that the unpaired electron is trapped at one vanadium atom and 1/16 of the spin density is delocalized onto the second vanadium atom. The species 1` is probably another form of the monoprotonated species. The EPR spectra show that some of 2 transform into 1 and some of 0 transform into 1` in the solid state at low temperatures. It is suggested that proton transfer between the heteropolyanion and water molecues in the solid state is involved in these transformations.