Exploration of the Atomic Pathway of Seed-Mediated Growth from Icosahedral [Au(SR)] to Bi-Icosahedral Au(SR) and Au(SR) Clusters Based on the 2 Hopping Mechanism.

Size growth is ubiquitous in the gold nanocluster synthesis. However, the atomic-level mechanism of seed-mediated growth of gold clusters remains mysterious. In this study, the seed-mediated growth pathway from the icosahedral [Au(SR)] cluster to the bi-icosahedral Au(SR) and Au(SR) clusters is studied based on the two-electron (2) hopping mechanism. First, atomic structures of three key intermediate clusters, [Au(SR)], [Au(SR)], and Au(SR), are predicted based on the 2-unit decomposition strategy. The theoretically simulated UV-Vis spectra based on the predicted structure model of [Au(SR)] and [Au(SR)] matched well with the experimental curves reported previously. Based on the predicted intermediate cluster structures, the size growth pathway from the eight-electron (8) [Au(SR)] cluster to 14-electron (14) Au(SR) and 18-electron (18) Au(SR) clusters is determined. In the step of formation of bi-icosahedral Au(SR) from icosahedral [Au(SR)], two Au units are first formed. The third 2 hopping step results in formation of an icosahedron unit. The present studies offered new insights into the formation and size conversion mechanism of ligand-protected gold nanoclusters containing icosahedral cores.