Synthesis and the Origin of the Stability of Thiolate-Protected Au130 and Au187 Clusters

Two stable thiolate-protected gold clusters (Au-SR), Au130 and Au187 clusters, were synthesized to obtain a better understanding of the size dependence of the origin of the stability of Au-SR clusters. These clusters were synthesized by employing different preparation conditions from those used to synthesize previously reported magic gold clusters; in particular, a lower RSH to AuCl4(-) molar ratio (AuCl4(-)/RSH = 1:1) was used than that used to prepare Au25(SR)18, Au38(SR)24, Au68(SR)34, Au102(SR)44, and Au144(SR)60 (id. = 1:4-12). The two clusters thus synthesized were separated from the mixture by high-performance liquid chromatography with reverse-phase columns. Mass spectrometry of the products revealed the presence of two clusters with chemical compositions of Au130(SC12H25)50 and Au187(SC12H25)68. The origin of the stability of these two clusters and the size dependence of the origin of the stability of thiolate-protected gold clusters were discussed in terms of the total number of valence electrons.