Self-inhibition phenomena in the electroreduction of hexamolybdocobaltate(III): A combined experimental and computational study

Reduction of a heteropolyanion (HPA) of the Anderson type ([CoMo6O24H6]3−) at a mercury electrode has been studied at different temperatures by using the polarographic technique. The results have been interpreted in terms of self-inhibition phenomena, which disclose non-monotonous dependence on the electrode charge. The adsorption interaction of the oxidized and reduced forms of HPA with the electrode surface was described in the framework of cluster model. The quantum chemical calculations were performed at the Density Functional Theory level. The distance-dependent electronic transmission coefficients were computed for three different orientations of [CoMo6O24H6]3− relative to the mercury surface. The planar orientation was found to be the least preferable from the viewpoint of both the adsorption energy and the orbital overlap. The experimental results have been explained qualitatively assuming the interplay between two orientations of the reduced form of HPA. The lateral interactions within the adlayer of anions (co-adsorbed with cations) were shown to be attractive and play an important role in self-inhibition.