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

The conventional synthetic methodology of atomically precise gold nanoclusters using reduction in solutions offers only thermodynamically most stable nanoclusters. We report herein a solubility-driven isolation strategy to access the synthesis of a metastable gold cluster. The cluster, with the composition of [Au 9 (PPh 3 ) 8 ] + ( 1 ), displays an unusual, nearly perfect body-centered-cubic (bcc) structure. As revealed by ESI-MS and UV/Vis measurement, the cluster is metastable in solution and converts to the well-known [Au 11 (PPh 3 ) 8 Cl 2 ] + ( 2 ) within just 90 min. DFT calculations revealed that while both 1 and 2 are eight-electron superatoms, there is a driving force to convert 1 to 2 as shown by the increased cohesion and larger HOMO-LUMO energy gap of 2 . The isolation and crystallization of the metastable gold cluster were achieved in a biphasic reaction system in which reduction of gold precursors and crystallization of 1 took place concurrently. This synthetic protocol represents a successful strategy for investigations of other metastable species in metal nanocluster chemistry.