Stibine-protected Au13 nanoclusters: syntheses, properties and facile conversion to GSH-protected Au25 nanocluster

Abstract

Monostibine-protected ionic Au₁₃ nanoclusters, namely, [Au₁₃(L)₈(Cl)₄][Cl] (L= SbPh₃, 2a·Cl; Sb(p-tolyl)₃, 2b·Cl) were prepared by the direct reduction of Au(L)Cl with NaBH₄ in dichloromethane. Anion exchange with 2a·Cl afforded [Au₁₃(SbPh₃)₈(Cl)₄][X] (X = PF₆, 2a·PF₆; BPh₄, 2a·BPh₄). All these have been characterized by multinuclear NMR, ESI-MS and UV-Vis spectroscopy. Crystallographic analysis of 2a·BPh₄ reveals that the cation possesses C_2v symmetry and the tridecagold core adopts a closed icosahedron configuration. The weaker coordinating ability of the stibine ligands leads to the ready reaction of 2b·Cl with PPh₃ or glutathione (GSH) to form the smaller phosphine-protected cluster [Au₁₁(PPh₃)₈Cl₂][Cl] or larger thiolate-protected cluster Au₂₅(SG)₁₈, respectively. In the latter reaction, the addition of a small amount (0.5 to 3.5 equivalents) of a suitable oxidant such as K₃(Fe(CN)₆ accelerates the conversion rate significantly.