Mechanism of Nucleation of Gold(I) Thiolate Oligomers into Gold–Thiolate Nanoclusters

The mechanism of reductive synthesis of gold–thiolate nanoclusters from gold­(I)–thiolate oligomers under boron hydride (BH₄^–) reduction is studied based on ab initio molecular dynamics (AIMD) simulations and density functional theory (DFT) calculations. The AIMD simulations show that the interaction between BH₄^– and the gold­(I)–thiolate oligomers leads to formation of active intermediates containing an Au–H or an Au–H–Au moiety, instead of direct formation of HSR and Au–Au bonds. The active intermediates interact with the gold­(I)–thiolate oligomers or other active intermediates to form Au–Au bonds and 2e^– building blocks. In the present studies, the pathways of formation of 2e^– building blocks from the active intermediate species are proposed and verified by the DFT calculations, which indicate that the hydride on Au–H and Au–H–Au moieties acts as a nucleophilic agent to attack gold atoms and lead to formation of new Au–Au bonds. The newly discovered nucleation mechanism is applied to understand the formation of 2e^– cluster Au₁₅(SR)₁₃ and 4e^– cluster Au₁₆(SR)₁₂.