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

Abstract

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.