Exploration of Formation and Size‐Evolution Pathways of Thiolate‐Gold Nanoclusters in the CO‐Directed [Au 25 (SR) 18 ] − Synthesis

An intermolecular association and decarboxylation mechanism is proposed to understand the experimental evidence of the stepwise 2 e − 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 2 e − –8 e − gold nanoclusters in the CO‐directed [Au 25 (SR) 18 ] − synthesis. With these established reaction equations, atomic pathways of three prototype cluster‐size evolution reactions are comprehensively explored in the course of [Au 25 (SR) 18 ] − synthesis, namely, the conversion of 0 e − homoleptic Au (I) ‐SR complexes to the 2 e − intermediate Au 15 (SR) 13 cluster, the size‐evolution of 2 e − Au 15 (SR) 13 cluster to the 4 e − –8 e − cluster (stepwise 2 e − ‐hopping), and the isoelectronic addition reaction of [Au 23 (SR) 16 ] − to the [Au 25 (SR) 18 ] − . The studies reveal that the CO can combine with the Au(I)‐complex to form [Au x (SR) x ‐COOH] − species in the alkaline condition, which acts as the active precursors in the 2 e − 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 2 e − reduction in the conventional “NaBH 4 reduction” system.