Unusually Fast Electron and Anion Transport Processes Observed in the Oxidation of “Electrochemically Open” Microcrystalline [{M(bipy)2}{M‘(bipy)2}(μ-L)](PF6)2 Complexes (M, M‘ = Ru, Os; bipy = 2,2‘-Bipyridyl; L = 1,4-Dihydroxy-2,5-bis(pyrazol-1-yl)benzene Dianion) at a Solid−Electrode−Aqueous Electrolyte Interface

Abstract

The oxidation of a series of bridged dinuclear metal complexes [{M(bipy)2}{M‘(bipy)2}(μ-L)]2+ (M, M‘ = Ru, Os; bipy = 2,2‘-bipyridyl; L = 1,4-dihydroxy-2,5-bis(pyrazol-1‘-yl)benzene dianion) in microcrystalline solid form has been studied at the basal plane pyrolytic graphite electrode−aqueous electrolyte interface. The solid materials undergo unusually rapid and essentially exhaustive electrolysis even under fast scan rate conditions of cyclic voltammetry via two one-electron oxidation charge-transfer steps: [{M(bipy)2}{M‘(bipy)2}(μ-L)]X2(solid) + X-(solution) ⇄ [{M(bipy)2}{M‘(bipy)2}(μ-L)]X3(solid) + e- (step 1); [{M(bipy)2}{M‘(bipy)2}(μ-L)]X3(solid) + X-(solution) ⇄ [{M(bipy)2}{M‘(bipy)2}(μ-L)]X4(solid) + e- (step 2). To maintain charge neutrality, the solid-state charge-transfer processes are coupled to rapid insertion/expulsion of anions from/to the aqueous electrolyte solution phase (X- = PF6-, ClO4-, SCN-, or NO3-). The conclusion is reached that “electrochemically open” solid-state structural fea...