Thiolate-protected gold clusters (Aun(SR)m) have attracted considerable attention as functional nanomaterials in a wide range of fields. A ligand-exchange reaction has long been used to functionalize these clusters. In this study, we separated products from a ligand-exchange reaction of phenylethanethiolate-protected Au24Pd clusters (Au24Pd(SC2H4Ph)18), in which Au25(SR)18 is doped with palladium, into each coordination isomer with high resolution by reversed-phase high-performance liquid chromatography. This success has enabled isomer distributions of the products to be quantitatively evaluated. We evaluated quantitatively the isomer distributions of products obtained by the reaction of Au24Pd(SC2H4Ph)18 with thiol, disulfide, or diselenide. The results revealed that the exchange reaction starts to occur preferentially at thiolates that are bound directly to the metal core (thiolates of a core site) in all reactions. Further study on the isomer-separated Au24Pd(SC2H4Ph)17(SC12H25) revealed that clusters vary the coordination isomer distribution in solution by the ligand-exchange reaction between clusters and that control of the coordination isomer distribution of the starting clusters enables control of the coordination isomer distribution of the products generated by ligand-exchange reactions between clusters. Au24Pd(SC2H4Ph)18 used in this study has a similar framework structure to Au25(SR)18, which is one of the most studied compounds in the Aun(SR)m clusters. Knowledge gained in this study is expected to enable further understanding of ligand-exchange reactions on Au25(SR)18 and other Aun(SR)m clusters.

This study reports improvements in the ligand-exchange reactivity of phenylethanethiolate-protected Au 25 cluster (Au 25 (SC 2 H 4 Ph) 18 ) following Ag or Cu incorporation. Following the synthesis of Au 25−x M x (SC 2 H 4 Ph) 18 (M = Au, Ag, Cu, or Pd), we determined the ligand-exchange reaction rates, using octanethiol (C 8 H 17 SH) as the exchange ligand, by employing mass spectrometry. The results show that incorporating Ag and Cu enhances the ligand-exchange reactivity of the clusters. On the basis of density functional theory calculations, it is concluded that the elevated reactivity of Au 25−x M x (SC 2 H 4 Ph) 18 (M = Ag or Cu) results from the more highly positive charge density of metal atoms in the staple upon Ag or Cu substitution. In addition, in the presence of Au 25−x M x (SC 2 H 4 Ph) 18 (M = Ag or Cu; x ≠ 0), an improvement in the ligand-exchange reaction rate was also observed for Au 25 (SC 2 H 4 Ph) 18 , even though this cluster does not include a heteroatom. This unexpected behavior is attributed to the contribution of a chemical reaction between clusters. These findings are expected to deepen our understanding of ligand-exchange reactions, and lead to design guidelines for the creation of Au n (SR) m clusters exhibiting new chemical compositions and functions, using this reaction.