Thiol ligand-induced transformation of Au_(38)(SC_2H _4Ph)_(24) to Au_(36)(SPh- t -Bu)_(24)

摘要

We report a disproportionation mechanism identified in the transformation of rod-like biicosahedral Au_(38)(SCH_2CH_2Ph) _(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)(SCH_2CH_2Ph)_(24) with bulkier 4-tert-butylbenzenethiol (TBBT) until a certain extent starts to trigger structural distortion of the initial biicosahedral Au_(38)(SCH _2CH_2Ph)_(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., Au40(TBBT)_(m+2)(SCH_2CH_2Ph) _(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(SCH_2CH_2Ph) _(24)-m. The reaction kinetics on the Au_(38)(SCH _2CH_2Ph)_(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 Au _(36)(TBBT)_(24) are interpreted on the basis of density functional theory simulations.