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 Au-38(SCH2CH2Ph)(24) to tetrahedral Au-36(TBBT)(24) nanoclusters. Time-dependent mass spectrometry and optical spectroscopy analyses unambiguously map out the detailed size-conversion pathway. The ligand exchange of Au-38(SCH2CH2Ph)(24) with bulkier 4-tert-butylbenzenethiol (TBBT) until a certain extent starts to trigger structural distortion of the initial biicosahedral Au-38(SCH2CH2Ph)(24) structure, leading to the release of two Au atoms and eventually the Au-36(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., Au-40(TBBT)(m)(SCH2CH2Ph)(24-m), was concurrently observed as an intermediate, which was the result of addition of two Au atoms and two TBBT ligands to Au-38(TBBT)(m)(SCH2CH2Ph)(24-m). The reaction kinetics on the Au-38(SCH2CH2Ph)(24) to Au-36(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.