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