A DFT study on the electronic and redox properties of [X₈V ₁₄O₅₀]^n- (X = Si^IV, Ge^IV, P^V, and As^V)

The electronic and redox properties of the title polyanions have been calculated by means of density functional theory (DFT). These were unrestricted open-shell systems with electronic configuration of d¹ of V. In this behalf, energies and compositions of α-LUMO, β-LUMO, α-HOMO, and β-HOMO were also analyzed. First of all, electronic and redox properties of vanadosilicate [Si₈V₁₄O₅₀] ^12- (system 1) were calculated and then Si^IV was substituted with Ge^IV, P^V, and As^V for further investigations of systems 2, 3, and 4, respectively. The substitution greatly modifies the electronic properties as α-LUMOs are quite different in all the studied systems. The α-LUMO is mainly composed of V and O in system 1, V and Ge in system 2, V and O in system 3, and As, O, and V in system 4. The alpha HOMO-LUMO energy gaps are greatly reduced in systems 2, 3, and 4 as compared with system 1. The system 4 [As₈V₁₄O ₅₀]^4- has minimal value of total bonding energy, whereas system 2 [Ge₈V₁₄O₅₀]^12- has maximal, so energetically system 4 is more favourable than the others. After the first reduction, α-LUMO in [Si₈V₁₄O₅₀] ^14- is made up of V and Si, β-LUMO in [Ge₈V ₁₄O₅₀]^13- is concentrated on V and Ge, β-LUMO in [P₈V₁₄O₅₀]^5- is composed of V only, whereas β-LUMO in [As₈V₁₄O ₅₀]^5- is delocalized over V, O, and As with almost the same contribution of all three atoms.