Size Growth of Au₄Cu₄: From Increased Nucleation to Surface Capping

The size conversion of atomically precise metal nanoclusters is fundamental for elucidating structure-property correlations. In this study, copper salt (CuCl)-induced size growth from [Au 4 Cu 4 (Dppm) 2 (SAdm) 5 ] + (abbreviated as [Au 4 Cu 4 S 5 ] + ) to [Au 4 Cu 6 (Dppm) 2 (SAdm) 4 Cl 3 ] + (abbreviated as [Au 4 Cu 6 S 4 Cl 3 ] + ) (SAdmH = 1-adamantane mercaptan, Dppm = bis-(diphenylphosphino)methane) was investigated via experiments and density functional theory calculations. The [Au 4 Cu 4 S 5 ] + adopts a defective pentagonal bipyramid core structure with surface cavities, which could be easily filled with the sterically less hindered CuCl and CuSCy (i.e., core growth) (HSCy = cyclohexanethiol) but not the bulky CuSAdm. As long as the Au 4 Cu 5 framework is formed, ligand exchange or size growth occurs easily. However, owing to the compact pentagonal bipyramid core structure, the latter growth mode occurs only for the surface-capped [Au 4 Cu 6 (Dppm) 2 (SAdm) 4 Cl 3 ] + structure (i.e., surface-capped size growth). A preliminary mechanistic study with density functional theory (DFT) calculations indicated that the overall conversion occurred via CuCl addition, core tautomerization, Cl migration, the second [CuCl] addition, and [CuCl]-[CuSR] exchange steps. And the [Au 4 Cu 6 (Dppm) 2 (SAdm) 4 Cl 3 ] + alloy nanocluster exhibits aggregation-induced emission (AIE) with an absolute luminescence quantum yield of 18.01% in the solid state. This work sheds light on the structural transformation of Au–Cu alloy nanoclusters induced by Cu(I) and contributes to the knowledge base of metal-ion-induced size conversion of metal nanoclusters.