Synergistic Effect of Bridging Thiolate and Hub Atoms for the Aromaticity Driven Symmetry Breaking in Atomically Precise Gold Nanocluster.

The symmetry of atomically precise nanoclusters is influenced by the specific geometry of the kernel and the arrangement of staple motifs. To understanding the role of ligand and its effect on the breaking of symmetry during ligand exchange transformation, it is necessary to have a mechanism of transformation in an atomically precise manner. Herein, we report the structural transformation from bipyramidal kernel to icosahedral kernel via ligand exchange. The transformation of [Au23(CHT)16]- to [Au25(2-NPT)18]- through ligand (aromatic) exchange revealed two important principles. First, the combined effort of experimental and theoretical study on structural analysis elucidated the mechanism of this structural transformation where "bridging thiolate" and "hub" gold atoms play a crucial role. Second, we have found that the higher crystal symmetry of the Au23 cluster is broken to lower crystal symmetry during the ligand exchange process. This showed that during ligand exchange, the hub atoms and μ3-S atoms get distorted and contributed to the ligand-staple motif formation. These phenomena specified that the ligand effects might be the pivotal factor to impose lower symmetry of the crystal system in the product clusters.