Tetratungsten Oxide Clusters W₄O_<i>n</i>^−/0 (<i>n</i> = 10−13): Structural Evolution and Chemical Bonding

Density functional theory (DFT) calculations are carried out to investigate the electronic and structural properties of a series of tetratungsten oxide clusters, W₄O_<i>n</i>^−/0 (<i>n</i> = 10−13). Generalized Koopmans’ theorem is applied to predict the vertical detachment energies and simulate the photoelectron spectra (PES). A large energy gap (∼2.9 eV) is observed for the stoichiometric W₄O₁₂ cluster, which reaches the bulk value. The calculations suggest that W₄O₁₂^−/0 have the planar eight-membered ring structures, in which each tungsten atom is tetrahedrally coordinated with two bridging O atoms and two terminal O atoms. W₄O₁₀^−/0 and W₄O₁₁⁻ can be viewed as removing two and one terminal O atoms from W₄O₁₂^−/0, respectively. The W₄O₁₁ neutral is an interesting species, which possesses the pentabridged structure. We show that W₄O₁₁⁻ contains a localized W³⁺ site, which can readily react with O₂ to form the W₄O₁₃⁻ cluster, whereas the corresponding neutral W₄O₁₃ can be viewed as replacing a terminal oxygen in W₄O₁₂ by a peroxo O₂ unit. Molecular orbital analyses are performed to analyze the chemical bonding in the tetratungsten oxide clusters and to elucidate their electronic and structural evolution.