Transport and electron transfer kinetics of polyoxovanadate-alkoxide clusters

A family of four polyoxovanadate-alkoxide (POV-alkoxide) clusters was prepared and electrochemical techniques were used to evaluate diffusion coefficients and electron transport across a range of oxidation states. Synthetic routes were developed to increase the alkyl chain length of the [V₆O₇(OR)₁₂] cores, increasing R from the previously reported R = CH₃, C₂H₅ to R = C₃H₇, C₄H₉. Whereas increasing chain length may enhance solubility, such modifications may also hinder diffusion and electron transfer by shielding the core, thus we experimentally determined these parameters using both cyclic voltammetry and rotating disk voltammetry. Increasing the alkyl chain length of the POV-alkoxide nanostructures from methoxide to butoxide changes the solubility from 0.205 to 0.297 M in acetonitrile. Although some variations in diffusion coefficients and heterogeneous electron transfer rate constants were observed across the suite of oxidation states from species to species, they range from 0.14 × 10^-5 cm²/s to 2.24 × 10^-5 cm²/s for D0 and 0.56 × 10^-3 cm/s to 209.00 × 10^-3 cm/s for khet. An increased chain length did not result in lower diffusion coefficients. Thus, we conclude that between C1 and C₄ chains, no shielding of the redox core occurs, nor is transport through solution systematically hindered.