Simplified Preparations and Electrochemical Behavior of Two Chromium-Substituted Heteropolytungstate Anions
Simplified preparative procedures are described for the generation of α-[PW_(11)O_(39)Cr^(III)(OH_2)]^(4-) and α2-[P_2W_(11)O_(61)Cr^(III)(OH_2)]^(7-) anions which can be readily oxidized, chemically or electrochemically, to α-[PW_(11)O_(39)Cr^(V)O]^(4-) and α2-[P_2W_(17)O_(61)Cr^(V)O]^(7-). The oxidized complexes are stable in aqueous solutions. They react with benzyl or ethyl alcohol, but the rates of the oxidations are too slow to make the Cr(V) derivatives attractive as electrocatalysts. The voltammetry of the Cr^(V)/Cr^(III) couples is only quasi-reversible, but approximate formal potentials with their pH dependencies are reported. Diffusion coefficients evaluated for the polyanions show the larger anion to diffuse more slowly and neither anion to be highly hydrated.
© 1994 American Chemical Society. Received August 27, 1993. This work was supported by a grant from the ONR/DARPA.