Elucidation of the Fundamental Properties of Thiolate-protected Metal Clusters by HPLC

Metal clusters composed of several to hundreds of metal atoms, having diameters of less than 2 nm, exhibit physical and chemical properties and functions unlike those of the corresponding bulk metals. Thiolate (SR)-protected metal clusters have been one of the most intensively studied types of metal clusters to date, since these metal clusters show great promise as functional nanomaterials. We have studied these clusters based on common analysis methods used by many other research groups. Simultaneously, we have also been actively working on applying high-performance liquid chromatography (HPLC) to the analysis of these clusters. Consequently, we have succeeded in systematically isolating a series of SR-protected gold clusters and their heteroatom-substituted clusters. By realizing such high-resolution separations, we have gained many new insights, including following into these clusters: 1) heteroatom substitution effects on the electronic structures and the experimental condition dependence of isomer distributions in hydrophobic SR-protected alloy clusters; 2) the mechanism of ligand-exchange reactions in hydrophobic metal clusters; 3) the chemical composition of products in hydrophilic metal clusters. We expect that the use of HPLC-based separation, shown in this account, leads to many more new findings concerning SR-protected metal clusters. Thus, we expect that these separation methods will be widely used in future studies of SR-protected metal clusters.