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 [Au 6 (dppp) 4 ] 2+ to [Au 8 (dppp) 4 Cl 2 ] 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 Au 6 structure, resulting in the high Au(core)−Au(corner) bond cleavage activity and the subsequent formation of [Au 2 (dppp) 2 Cl] + and [Au 4 (dppp) 2 Cl] + fragments. Then, the dimerization of two Au 4 fragments and the rearrangement of the diphosphine coordination occur to generate the thermodynamically stable [Au 8 (dppp) 4 Cl 2 ] 2+ products. The proposed mechanism agrees with the experimental outcome for the fast reaction rate and the residual of the Au 2 components. Specifically, a multivariate linear regression analysis indicates the strong correlation of the oxidation potential of Au 6 , Au 8 , Au 23 , and Au 25 clusters with the HOMO energy, the number of Au atoms, and cluster charge state. The main conclusions [e.g., oxidationinduced 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.

Chemical Flexibility of Atomically Precise Metal Clusters

“…While calculating DFT, the oxidation-induced growth from Au 6 to Au 8 -1 was studied, and the results show the following sequence of successive oxidation → Cl – coordination → oxidation → Cl – coordination, which activates the Au 6 structure. This process leads to the high bond cleavage activity of Au core –Au corner and the subsequent formation of [Au 2 (dppp) 2 Cl] + and [Au 4 (dppp) 2 Cl] + fragments . Then two Au 4 fragments dimerize, and the diphosphine coordination rearranges to form the thermodynamically stable Au 8 -1 .…”

“…However, due to the distinctly physical-chemical properties (e.g., the steric hindrance, ,,,, electron-withdrawing/donating, and hydrophobicity and hydrophilicity , ) of different groups of inducers, the original structures may not be the most stable state, and then the structural transformation takes place. (iii) The redox process of clusters is accompanied by reduction and increase of NC electrons, which can cause significant changes in the cluster geometry, in particular, the change of the electronic structure of superatom NCs will induce the structural transformation to a more stable configuration (refs , , , − , and − ). (iv) The inducer does not directly react with the cluster, only changes the physical-chemical environment of the cluster, such as solvent polarity, pH, temperature, light, electric field, and external pressure. ,,,− …”

“…308 Then two Au 4 fragments dimerize, and the diphosphine coordination rearranges to form the thermodynamically stable Au 8 -1. Subsequently, this system was extended to the transition between Au 6 and [Au 11 (dppp) 5 ] 3+ (Au 11 , 8e) and that between Au 8 and Au 11 , all caused by the reaction environment 266.…”

The Pivotal Radical Intermediate [Au21(SR)15]+ in the Ligand-Exchange-Induced Size-Reduction of [Au23(SR)16]− to Au16(SR)12

“…Continuing our recent endeavors to understand the kinetic profiles of the cluster conversion reactions, − herein we explored the reaction and especially the kinetic profiles of the reaction of [Au 23 (CHT) 16 ] − with HSAdm. It was found that during the 16 h conversion of [Au 23 (CHT) 16 ] − to Au 16 (SR) 12 , Au 21 represents a pivotal intermediate state.…”