Solubility-Driven Isolation of a Metastable Nonagold Cluster with Body-Centered Cubic Structure

The conventional synthetic methodology for atomically precise gold nanoclusters by using reduction in solution offers only the thermodynamically most stable nanoclusters. Herein, a solubility-driven isolation strategy is reported to access a metastable gold cluster. The cluster, with the composition of [Au-9(PPh3)(8)](+)(1), displays an unusual, nearly perfect body-centered cubic (bcc) structure. As revealed by ESI-MS and UV/Vis measurements, the cluster is metastable in solution and converts to the well-known [Au-11(PPh3)(8)Cl-2](+)(2) within just 90 min. DFT calculations revealed that although both1and2are eight-electron superatoms, there is a driving force to convert1to2as shown by the increased cohesion and larger HOMO-LUMO energy gap of2. The isolation and crystallization of the metastable gold cluster were achieved in a biphasic reaction system in which reduction of gold precursors and crystallization of1took place concurrently. This synthetic protocol represents a successful strategy for investigations of other metastable species in metal nanocluster chemistry.