Insights into the redox landscape of polyoxovanadate-alkoxide species

Polyoxovanadate-alkoxides are a class of polynuclear earth-abundant transition metal compounds with highly tunable catalytic, redox, and magnetic properties. These species are ideal electroactive molecular agents for environmentally friendly energy storage applications, such as non-aqueous redox flow batteries. As such, it is fundamental to understand structure-redox relationships in the multielectron redox profiles of polyoxovanadate-alkoxides species. Here, we studied the redox properties of monomeric vanadate-alkoxide species that control the formation of two distinct chemical spaces with mix-valent clusters and fully reduced cyclic species. The accuracy of various density functional theory approximations and basis sets choices was benchmarked against domain-based local pair natural orbital coupled cluster, specifically DLPNO-CCSD(T). To further confirm the broader applicability of density functional theory in higher nuclearity species, we studied the redox profile of [(VV6-nVIVnO₆)(O)(OCH₃)₁₂]^4-n, [(Nb = O)(VV5-nVIVnO₅)(O)(OCH₃)₁₂]^4-n, [(M-OCH₃)(VV5-nVIVnO₅)(O)(OCH₃)₁₂]^4-n (M = Ti, Zr, or Hf), and [(Fe-Cl)(VV5-nVIVnO₅)(O)(OCH₃)₁₂]^3-n hexanuclear polyoxovanadate-alkoxide species. The calculated redox profiles of these species were in good agreement with experimental data with an average absolute error of 0.11 V.