Thiol Ligand-Induced Transformation of Au₃₈(SC₂H₄Ph)₂₄ to Au₃₆(SPh‑t‑Bu)₂₄

We report a disproportionation mechanism identified in the transformation of rod-like biicosahedral Au₃₈(SCH₂CH₂Ph)₂₄ to tetrahedral Au₃₆(TBBT)₂₄ nanoclusters. Time-dependent mass spectrometry and optical spectroscopy analyses unambiguously map out the detailed size-conversion pathway. The ligand exchange of Au₃₈(SCH₂CH₂Ph)₂₄ with bulkier 4-tert-butylbenzenethiol (TBBT) until a certain extent starts to trigger structural distortion of the initial biicosahedral Au₃₈(SCH₂CH₂Ph)₂₄ structure, leading to the release of two Au atoms and eventually the Au₃₆(TBBT)₂₄ nanocluster with a tetrahedral structure, in which process the number of ligands is interestingly preserved. The other product of the disproportionation process, i.e., Au₄₀(TBBT)_m+2(SCH₂CH₂Ph)_24–m, was concurrently observed as an intermediate, which was the result of addition of two Au atoms and two TBBT ligands to Au₃₈(TBBT)_m(SCH₂CH₂Ph)_24–m. The reaction kinetics on the Au₃₈(SCH₂CH₂Ph)₂₄ to Au₃₆(TBBT)₂₄ conversion process was also performed, and the activation energies of the structural distortion and disproportionation steps were estimated to be 76 and 94 kJ/mol, respectively. The optical absorption features of Au₃₆(TBBT)₂₄ are interpreted on the basis of density functional theory simulations.