Experimental and theoretical study of the reactions between vanadium-silicon heteronuclear oxide cluster anions with n -butane

Vanadium and silicon heteronuclear oxide cluster anions V _xSi_yO_z^- (x + y ≥ 2, z ≥ 4) are prepared by laser ablation and reacted with n-butane (C₄H ₁₀) in a fast flow reactor. A time-of-flight mass spectrometer is used to detect the cluster distribution before and after the reactions. The observation of hydrogen-containing products (V₂O₅) _m(SiO₂)_nOH^- (m = 1, n = 1-4; m = 2, n = 1) strongly suggests the following reactions: (V₂O ₅)_m(SiO₂)_nO^- + C ₄H₁₀ → (V₂O₅) _m(SiO₂)_nOH^- + C₄H ₉. Although V₂O₆^- is produced in the cluster source, no V₂O₆H^- product is produced under the same experimental condition. It indicates that specific heteronuclear oxide clusters V₂O₅(SiO₂)_1-4O ^- and (V₂O₅)₂SiO₂O ^- are more reactive than the homonuclear oxide cluster V ₂O₆^- (or V₂O₅O ^-). Density functional theory (DFT) calculations are performed to study reaction mechanisms of V₂O₅SiO₂O ^- (or V₂SiO₈^-) + C₄H ₁₀. The calculated results are in good agreement with the experimental observations. The structural and bonding properties of (V ₂O₅)_m(SiO₂)_nO ^- (m = 1, n = 1-4; m = 2, n = 1) are also investigated by the DFT calculations. The unpaired electron in each of the clusters is mainly distributed over one or two O atoms (2p orbitals) bonded with Si rather than V atom(s). Furthermore, the experimentally observed higher reactivity of the V-Si heteronuclear oxide cluster (V₂O₅)_m(SiO ₂)_nO^- over the homonuclear V₂O ₆^- in the reaction with C₄H₁₀ is interpreted based on the theoretical results.