Identifying the Real Chemistry of the Synthesis and Reversible Transformation of AuCd Bimetallic Clusters

The capability of precisely constructing bimetallic clusters with atomic accuracy provides exciting opportunities for establishing their structure-property correlations. However, the chemistry (the charge state of precursors, the property of ligands, the amount of dopant, and so forth) dictating the fabrication of clusters with atomic-level control has been a long-standing challenge. Herein, based on the well-defined Au₂₅(SR)₁₈ cluster (SR = thiolates), we have systematically investigated the factors of steric hindrance and electronic effect of ligands, the charge state of Au₂₅(SR)₁₈, and the amount of dopant that may determine the structure of AuCd clusters. It is revealed that [Au₁₉Cd₃(SR)₁₈]^- can be obtained when a ligand of smaller steric hindrance is used, while Au₂₄Cd(SR)₁₈ is attained when a larger steric hindrance ligand is used. In addition, negatively charged [Au₂₅(SR)₁₈]^- is apt to form [Au₁₉Cd₃(SR)₁₈]^- during Cd doping, while Au₂₄Cd(SR)₁₈ is produced when neutral Au₂₅(SR)₁₈ is used as a precursor. Intriguingly, the reversible transformation between [Au₁₉Cd₃(SR)₁₈]^- and Au₂₄Cd(SR)₁₈ is feasible by subtly manipulating ligands with different steric hindrances. Most importantly, by introducing the excess amount of dopant, a novel bimetallic cluster, Au₄Cd₄(SR)₁₂ is successfully fabricated and its total structure is fully determined. The electronic structures and the chirality of Au₄Cd₄(SR)₁₂ have been elucidated by density functional theory (DFT) calculations. Au₄Cd₄(SR)₁₂ reported herein represents the smallest AuCd bimetallic cluster with chirality.