Stibine-protected Au(13) nanoclusters: syntheses, properties and facile conversion to GSH-protected Au(25) nanocluster

Monostibine-protected ionic Au(13) nanoclusters, namely, [Au(13)(L)(8)(Cl)(4)][Cl] (L= SbPh(3), 2a·Cl; Sb(p-tolyl)(3), 2b·Cl) were prepared by the direct reduction of Au(L)Cl with NaBH(4) in dichloromethane. Anion exchange with 2a·Cl afforded [Au(13)(SbPh(3))(8)(Cl)(4)][X] (X = PF(6), 2a·PF(6); BPh(4), 2a·BPh(4)). All these have been characterized by multinuclear NMR, ESI-MS and UV-Vis spectroscopy. Crystallographic analysis of 2a·BPh(4) 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 PPh(3) or glutathione (GSH) to form the smaller phosphine-protected cluster [Au(11)(PPh(3))(8)Cl(2)][Cl] or larger thiolate-protected cluster Au(25)(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 K(3)(Fe(CN)(6) accelerates the conversion rate significantly.