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

The mechanism of reductive synthesis of gold-thiolatenanoclusters 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 AIMDsimulations show that the interaction between BH4-and the gold(I)-thiolate oligomers leads to formation of active intermediates containing anAu-HoranAu-H-Au moiety, instead of direct formation of HSR andAu-Au bonds. The active intermediates interact with the gold(I)-thiolateoligomers 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 andverified by the DFT calculations, which indicate that the hydride on Au-Hand Au-H-Au moieties acts as a nucleophilic agent to attack gold atomsand lead to formation of new Au-Au bonds. The newly discovered nucleation mechanism is applied to understand the formation of2e-cluster Au15(SR)13and 4e-cluster Au16(SR)12.