Unveiling the Formation Mechanism for Binary Semiconductor Nanoclusters: a Two-Step Pathway to a Double-Shell Structured Copper Sulfide Nanocluster

This work represents an important step in the quest to unveil the formation mechanism of atomically precise binary semiconductor nanoclusters. In this study, we develop an acid-assisted C–S bond cleavage approach, wherein the C–S bonds in the metal thiolate precursor can be readily cleaved to release S^2– with the assistance of a suitable acid in the presence of Cu₂O as the catalyst. This process spontaneously fosters the formation of a [−Cu–S–Cu−] framework and promotes the structural growth into a high nuclearity assembly. Specifically, by employing Cu(I) tert-butyl thiolate ([CuS^tBu]_∞) and carboxylate acid CH₂CHCOOH as the copper/sulfur precursor and C–S bond “scissor”, a high-nuclearity nanocluster [S–Cu₅₆] (Cu₅₆S₁₂(OOCCHCH₂)₁₂(SC(CH₃)₃)₂₀) featuring a double-shell configuration has been effectively prepared in high yield. Importantly, the [CuS^tBu]_∞ precursor and the intermediate [S–Cu₁₄] (Cu₁₄(S^tBu)₈(OOCCHCH₂)₆) cluster have also been successfully isolated and structurally characterized, which ultimately enables the establishment of a two-step formation pathway for the [S–Cu₅₆] nanocluster. Furthermore, in contrast to conventional reduction synthetic routes for metal nanoclusters containing Cu(0) or Cu(I), the acid-assisted C–S bond cleavage approach represents an oxidation process with respect to the constituent metals, yielding highly charged Cu(II) cations in the copper sulfide nanocluster.