Substitution of O with a Single Au Atom as an Electron Acceptor in Al Oxide Clusters

Al atoms generally adopt the +3 oxidation state and form stoichiometric oxides such as Al₂O₃ in the bulk phase. Among small cationic gas-phase clusters, near-stoichiometric clusters such as Al₃O₄⁺, Al₃O₅⁺, Al₄O₆⁺, Al₄O₇⁺, Al₅O₇⁺, and Al₅O₈⁺ have been readily generated in experimental studies. However, when a single Au atom was included in the clusters, oxygen-deficient clusters such as AuAl₄O₅⁺ were formed in high abundance; in these clusters, the Au atom accepted electron density from the Al atoms. The geometrical structures and atomic charges in the clusters suggest that a single Au atom can substitute for O atoms in Al oxide clusters. This propensity originates from the high electron and low oxygen affinities, which, together, constitute an unusual property of Au.