Ambient Synthesis of Au144(SR)60 Nanoclusters in Methanol

We report a facile, one-pot method for synthesizing atomically monodisperse Au-144(SR)(60) nanoclusters under ambient conditions. In this method, gold salt precursor is first mixed with excess thiol and tetraoctylammonium bromide (TOABr) in methanol to form Au(I)-SR polymers. Then, Au(I)-SR is reduced by excess NaBH4 (aqueous solution) to form nanoclusters. Interestingly, the initially formed, polydisperse Au nanoparticles are size-focused into two monodisperse gold nanoclusters: Au-144(SR)(60) (major product) and Au-25(SR)(18) (side product) over a similar to 5 h period. The side product (Au-25(SR)(18)) can be easily removed by washing the product with acetone, giving rise to pure Au-144(SR)(60). This method is applicable to a number of thiol ligands, including PhC2H4SH and various CnH2n+1SH (where n = 4-8). Some critical parameters to obtain pure Au-144(SR)(60) have been identified, including the methanol solvent (as opposed to toluene traditionally used), large thiol-to-Au ratios (>= 4), the presence of O-2 and tetraoctylammonium halide (TOAX, where X = Br, Cl). The facile synthetic method and the product made by this method should largely contribute to the practical application of this new type of nanomaterial.