Synthesis and the Origin of the Stability of Thiolate-Protected Au130 and Au187Clusters

Two stable thiolate-protected gold clusters (Au-SR), Au-130 and Au-187 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 Au-25(SR)(18), AU(38)(SR)(24), AU(68)(SR)(34), Au-102(SR)(44), and Au-144(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 Au-130(SC12H25)(50) and Au-187(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.