On the Mechanism of the Reaction between Thiolate-Protected Gold Clusters and Molecular Oxygen: What is Activated?

The various energy pathways of Au-20(SCH3)(16) oxidation were simulated in the gas phase and on a CeO2 surface at the density functional theory/Perdew-Burke-Ernzerhof (DFT/PBE) level. Due to the high stability and strong Au-S bonds of the protected cluster, there was no stable complex with oxygen. Alternative processes were considered: oxidation of staple (AuSCH3)(x) fragments and the cluster, in which one, two, and three thiolate ligands were removed (Au-20(SCH3)(16-x), x = 1-3). It was shown that peroxide and superoxide complexes formed only if the cluster fragments reacted with singlet oxygen. Oxygen was sufficiently absorbed on Au-20(SCH3)(16-x). The structures of Au-20(SCH3)(16) and Au-20(SCH3)(16-x) on the CeOx surface were studied in detail. After deposition of the cluster on ceria, the thiolate ligands were lost. Oxygen was activated on Au-20(SCH3)(13)/CeOx near the particle-support interface (the adsorption energy was 112 kJ/ mol).