Single-ligand exchange on an Au–Cu bimetal nanocluster and mechanism

Abstract

An Au–Cu bimetallic nanocluster co-capped by selenolate and phosphine is obtained and its X-ray structure shows an icosahedral Au₁₃ kernel surrounded by three CuSe₂PPh₂Py motifs and one CuSe₃ motif, formulated as [Au₁₃Cu₄(PPh₂Py)₃(SePh)₉]. Interestingly, a single-ligand exchange process is observed in the growth reaction, in which an [Au₁₃Cu₄(PPh₂Py)₄(SePh)₈]⁺ intermediate is first formed, but a prolonged reaction leads to one PPh₂Py ligand being selectively replaced by a PhSe-ligand. DFT simulations reveal that both steric hindrance and bond dissociation energy have great effects on the single-ligand exchange reaction as well as the thermodynamics, which help to understand the mechanism of the ligand exchange. Temperature-dependent UV-vis absorption and photoluminescence (PL) properties of the Au–Cu nanocluster imply that the optical properties are mainly contributed by the metal core. Femtosecond time-resolved pump–probe analysis maps out further details of the PL process.