Exploration of Formation and Size-Evolution Pathways of Thiolate-Gold Nanoclusters in the CO-Directed [Au25(SR)18]-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-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 0e(-)homoleptic Au-(I)-SR complexes to the 2e(-)intermediate Au-15(SR)(13)cluster, the size-evolution of 2e(-)Au(15)(SR)(13)cluster to the 4e(-)-8e(-)cluster (stepwise 2e(-)-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 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(4)reduction system.

Automated summary

By proposing an intermolecular association and decarboxylation mechanism, the experimental evidence of stepwise 2e(-) hopping in reductant-assisted thiolate-gold cluster synthesis is successfully understood. A total of 19 molecular-like reaction equations are deduced to comprehensively explore the atomic pathways of cluster-size evolution, revealing the role of CO in the 2e(-) hopping process.