Symmetric Growth of Dual-Packed Kernel: Exploration of the Evolution of Au40(SR)24 to Au49(SR)27 and Au58(SR)30 Clusters via the 2e–-Reduction Cluster Growth Mechanism

Abstract

The symmetric and periodic growth of metal core and ligand shell has been found in a number of ligand-protected metal clusters. So far, the principle of symmetric growth has been widely used to understand and predict the cluster structure evolution. In this work, based on the experimentally resolved crystal structure of Au40(o-MBT)24 and Au49(2,4-DMBT)27 clusters and a newly proposed two-electron (2e–) reduction cluster growth mechanism, the evolution pathway from the quasi-face-centered-cubic (fcc)-structured Au40(SR)24 cluster to the dual fcc- and nonfcc-packed Au49(SR)27 and Au58(SR)30 clusters was studied. The current research has clarified two important issues of cluster structure evolution. First, the formation of the dual-packed fcc and nonfcc kernel structure has been rationalized based on a 2e—reduction-based seed-mediated cluster growth pathway. Second, it is found that the symmetrical growth does not necessarily lead to the formation of stable cluster structures. It was found that the formation of dual-packed kernels in the Au49(SR)27 cluster is favorable because of the stability of the intermediate cluster structures and the relatively high thermodynamic stability of the cluster itself. However, although the structure of Au58(SR)30 cluster conforms to the principle of symmetric growth, the tension between the ligand shell and the gold atom of the metal nucleus increases significantly during the cluster size evolution, and the stability of the intermediate clusters is poor, so the formation of the Au58(SR)30 cluster is unfavorable. This study also shows that the 2e–-reduction cluster growth mechanism can be used to explore the structural evolution and stability of thiolate-protected gold clusters.