Adsorption of O2 on Cationic Gold Clusters: Analyses on Bonding Strength and Extent of Activation

We explored the adsorption of O2 on cationic gold clusters by combining cluster reaction experiments and theoretical calculations. Under a mild condition, Au10+ can readily adsorb one O2 molecule forming Au10O2+; Au2+ and Au4+ are low-reactive, while the argon complexes Au2ArO2+ and Au4Ar1,2O2+ can easily form; all other sizes are inactive. Theoretical calculations indicate that the O2 on the linear or planar structures of Aun+ (n=2–7) and the planar isomers of Au8+ tends to be adsorbed in an end-on manner and non-activated, and so does the O2 on the large odd sizes of Aun+ with n=9, 11, and 13 determined to be three-dimensional structures. In marked contrast, the O2 on the three-dimensional isomer of Au8+ and the large even-numbered Aun+ with n=10, 12, and 14 tends to be adsorbed in a side-on manner and apparently activated. Observation of only Au2,4,10O2+, Au2ArO2+, and Au4ArO2+ in the present experiments can be well rationalized using the calculated bonding strengths and the kinetic factors.