Atomically precise preorganization of open metal sites on gold nanocluster with high catalytic performance.

The design and synthesis of gold nanoclusters with surface open sites are crucial for practical applications in catalysis. We have developed a "surface geometric mismatch" strategy by using mixed ligands of different type of hindrance. When bulky phosphine Ph 3 P and planar dipyridyl amine (Hdpa) are simultaneously used, the steric repulsion between the ligands will reduce the ligand coverage of gold clusters, therefore the coordinative unsaturation of gold atoms is attained. A well-defined access granted gold nanocluster [Au 23 (Ph 3 P) 10 (dpa) 2 Cl](SO 3 CF 3 ) 2 ( Au 23 , dpa = dipyridylamido) has been successfully synthesized. Single crystal structural determination reveals that Au 23 has eight uncoordinated gold atoms in the shape of a distorted bicapped triangular prism. The accessibility of the exposed Au atoms has been confirmed quantitatively by luminescent titration with 2-naphthalenethiol. Furthermore, this cluster has excellent performance toward selective oxidation of benzyl alcohol to benzaldehyde. This atomically precise cluster stays intact after the catalytic reaction, demonstrating its excellent stability due to the protection of negatively charged multidentate ligand dpa.