Impact of Anionic Dopants on H Atom Uptake at Polyoxovanadate-Alkoxide Surfaces

Proton-coupled electron transfer (PCET) is an important mechanism that defines the reactivity of H atom equivalents at reducible metal oxide (MO_x) surfaces. To better understand structure-function properties that dictate the thermochemistry and kinetics of PCET at MO_x surfaces, our group has employed polyoxovanadate-alkoxide (POV-alkoxide) complexes as molecular models of extended materials. In this work, we investigate the influence of anionic dopants on PCET reactivity in POV-alkoxides. We present the synthesis and characterization of two anion-substituted POV-ethoxides, [V₆O₆X(OC₂H₅)₁₂]^- (X = Cl or SCN). Reactivity of these assemblies with a potent H atom transfer reagent, 9,10-dihydrophenazine, in acetonitrile (MeCN) affords formation of the 2e^-/2H⁺ reduced species, [V₆O₆X(MeCN)(OC₂H₅)₁₂]^-. The identity of the (pseudo)halide dopant influences the rate of the reaction, wherein the thiocyanate-substituted species exhibits H atom uptake at rates 2× faster than its chloride congener, and 5× faster than the fully oxygenated assembly, [V₆O₇(OC₂H₅)₁₂]^-. Collectively, these results provide insight into the role the identify of the dopant plays in controlling the kinetics of H atom uptake/transfer at the surfaces of MO_x.