Exploration of the Atomic Pathway of Seed-Mediated Growth from Icosahedral [Au25(SR)18]− to Bi-Icosahedral Au38(SR)24 and Au44(SR)26 Clusters Based on the 2e– 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 [Au₂₅(SR)₁₈]^- cluster to the bi-icosahedral Au₃₈(SR)₂₄ and Au₄₄(SR)₂₆ clusters is studied based on the two-electron (2e^-) hopping mechanism. First, atomic structures of three key intermediate clusters, [Au₂₉(SR)₂₀]^-, [Au₃₃(SR)₂₂]^-, and Au₄₁(SR)₂₅, are predicted based on the 2e^--unit decomposition strategy. The theoretically simulated UV-Vis spectra based on the predicted structure model of [Au₂₉(SR)₂₀]^- and [Au₃₃(SR)₂₂]^- matched well with the experimental curves reported previously. Based on the predicted intermediate cluster structures, the size growth pathway from the eight-electron (8e^-) [Au₂₅(SR)₁₈]^- cluster to 14-electron (14e^-) Au₃₈(SR)₂₄ and 18-electron (18e^-) Au₄₄(SR)₂₆ clusters is determined. In the step of formation of bi-icosahedral Au₃₈(SR)₂₄ from icosahedral [Au₂₅(SR)₁₈]^-, two Au₄ units are first formed. The third 2e^- 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.