Photoinitiated Two-Electron Oxidation of Tris(1,10-phenanthroline)vanadium(II)

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The redox and photochemical properties of vanadium polypyridine complexes have been combined to achieve the first example of photoredox-initiated two-electron oxidation at a single transition-metal center. Cyclic voltammetry of V(phen)32+ (phen = 1,10-phenanthroline) in shows three reversible redox couples due to and V(phen)3+/°, with half-wave potentials of 0.09, -1.51, and -1.70 V, respectively, vs. Fc/Fc+ (Fc = ferrocene). Solutions of the vanadium(III) complex in CH3CN exhibit a single irreversible oxidation wave, which is probably associated with formation of a mononuclear vanadium(IV) complex. This electrogenerated vanadium(IV) species is also electroactive, showing quasi-reversible oxidation and reduction waves. Similar quasi-reversible waves observed in the V(phen)32+ voltammograms are attributable to the same species, formed by hydrolysis of V(phen)33+ and subsequent rapid oxidation. In buffered aqueous solutions (pH spontaneously reduces the electron acceptors MV2+ (methylviologen or and The vanadium-containing electron-transfer product is a V02+ complex, as identified by its ESR spectrum. Thus, irradiation of a solution (pH 8) of V(phen)32+ and MV2+ (X > 500 nm) leads to the one-electron photooxidation of V(phen)32+, followed by thermal electron transfer to produce VO2+. © 1987, American Chemical Society. All rights reserved.

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Inorganic Chemistry

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