Exploration of Formation and Size-Evolution Pathways of Thiolate-Gold Nanoclusters in the CO-Directed [Au (SR) ] Synthesis.

An intermolecular association and decarboxylation mechanism is proposed to understand the experimental evidence of the stepwise 2e hopping in the reductant-assisted thiolate-gold cluster synthesis. Based on the newly proposed intermolecular reaction mechanism, a total of 19 molecular-like reaction equations are deduced to account for the bottom-up formation of 2e -8e gold nanoclusters in the CO-directed [Au (SR) ] synthesis. With these established reaction equations, atomic pathways of three prototype cluster-size evolution reactions are comprehensively explored in the course of [Au (SR) ] synthesis, namely, the conversion of 0e homoleptic Au -SR complexes to the 2e intermediate Au (SR) cluster, the size-evolution of 2e Au (SR) cluster to the 4e -8e cluster (stepwise 2e -hopping), and the isoelectronic addition reaction of [Au (SR) ] to the [Au (SR) ] . The studies reveal that the CO can combine with the Au(I)-complex to form [Au (SR) -COOH] species in the alkaline condition, which acts as the active precursors in the 2e hopping cluster-size evolution process. Lastly, as a conceptual extension of the mechanistic studies of the CO-reduction system, a similar intermolecular reaction mechanism is proposed for the 2e reduction in the conventional "NaBH reduction" system.