Mechanistic Insights into Oxidation-Induced Size Conversion of [Au₆(dppp)₄]²⁺ to [Au₈(dppp)₄Cl₂]²

Oxidation-induced conversion of gold nanoclusters is an important strategy for preparing novel atomically precise clusters and elucidating the kinetic correlations of different clusters. Herein, the oxidation-induced growth from [Au₆(dppp)₄]²⁺ to [Au₈(dppp)₄Cl₂]²⁺ (reported by Konishi and co-workers) has been studied by density functional theory calculations. A successive oxidation → Cl^- coordination → oxidation → Cl^- coordination sequence occurs first to activate the Au₆ structure, resulting in the high Au(core)-Au(corner) bond cleavage activity and the subsequent formation of [Au₂(dppp)₂Cl]⁺ and [Au₄(dppp)₂Cl]⁺ fragments. Then, the dimerization of two Au₄ fragments and the rearrangement of the diphosphine coordination occur to generate the thermodynamically stable [Au₈(dppp)₄Cl₂]²⁺ products. The proposed mechanism agrees with the experimental outcome for the fast reaction rate and the residual of the Au₂ components. Specifically, a multivariate linear regression analysis indicates the strong correlation of the oxidation potential of Au₆, Au₈, Au₂₃, and Au₂₅ clusters with the HOMO energy, the number of Au atoms, and cluster charge state. The main conclusions [e.g., oxidation-induced Au(corner)-Au(core) bond activation, easy 1,2-P transfer steps, etc.] of this study might be widely applicable in improving our understanding of the mechanism of other cluster-conversion reactions.