Rotational Isomerism, Electronic Structures, and Basicity Properties of "Fully-Reduced" V14-type Heteropolyoxovanadates.

Abstract

We investigated computationally the α-, γ-, and β-isomeric structures, relative stabilities, and the electronic and basicity properties of magnetic [V(IV)14E8O50](12-) (hereafter referred to as {V14E8}) heteropolyoxovanadates (heteroPOVs) and their heavier chalcogenide-substituted [V(IV)14E8O42X8](12-) ({V14E8X8}) derivatives for E = Si(IV), Ge(IV), and Sn(IV) and X = S, Se, and Te. We used density functional theory (DFT) with scalar relativistic corrections in combination with the conductor-like screening model of solvation. The main purpose of this investigation is to introduce the structure-property relations in heteroPOVs as well as to assist the synthesis and molecular deposition of these molecular vanadium-oxide spin clusters on surfaces. "Fully-reduced" polyoxoanions {V14E8} and {V14E8X8} are virtually comprised of [V(IV)14O38](20-) {V14} skeletons of different symmetries, that is, D2d for α-, D2 for γ-, and D4h for β-isomers, which are stabilized by the four {E2O3}(2+) and four {E2OX2}(2+) moieties, respectively. Our DFT calculations reveal stability trends α > γ > β for polyoxoanions {V14E8} and {V14E8X8}, based on relative energies and HOMO-LUMO energy gaps. The α-isomeric polyoxoanions {V14E8} and {V14E8X8} with the high negative net charges may easily pick up protons at the terminal E-Ot and E-Xt sites, respectively, which is evidenced by strongly negative enthalpies of monoprotonation. Energetically favorable sites on polyoxoanions α-{V14E8} and α-{V14E8X8} for electrostatic pairing with countercations were also determined. Among β and γ isomers, the hitherto unknown γ-[V14Sn8O50](12-) and γ-[V14Sn8O42S8](12-) seem to be the most viable targets for isolation. Furthermore, these Sn-substituted polyoxoanions are of high interest for electrochemical studies because of their capability to act as two-electron redox catalysts.