Identification of Intermediate Au22(SR)4(SR′)14 Cluster on Ligand-Induced Transformation of Au25(SR)18 Nanocluster

We report the ligand-exchange-induced transformation from an icosahedral Au 25 (SR) 18 cluster (where SR = 2-phenylethanethiol (PET)) to a bitetrahedral Au 22 (SR) 4 (SR′) 14 cluster (where SR′ = 4- tert -butylbenzenethiol (TBBT)). This partial exchange of the ligands was achieved by controlling the concentration of the incoming TBBT ligand. Being a bulky and aromatic ligand, TBBT can efficiently distort the atomic structure of the Au 25 PET 18 cluster, resulting in Au 22 (PET) 4 (TBBT) 14, which is highly stable and considered to be an intermediate with a bitetrahedral structure. Time-dependent mass spectrometry and optical spectroscopy revealed the dissociation of the parent cluster and gave a deep insight on the ligand-exchange mechanism. Theoretical calculations and extended X-ray absorption fine structure studies confirm the formation of the Au 22 structure. Identifying the atomic structure of the intermediate species opens a new avenue to study the transformation of one cluster to another.