Combinatorial Identification of Hydrides in a Ligated Ag₄₀ Nanocluster with Noncompact Metal Core

No formation of bulk silver hydride has been reported. Until very recently, only a few silver nanoclusters containing hydrides have been successfully prepared. However, due to the lack of effective techniques and also poor stability of hydride-containing Ag nanoclusters, the identification of hydrides' location within Ag nanoclusters is challenging and not yet achieved, although some successes have been reported on clusters of several Ag atoms. In this work, we report a detailed structural and spectroscopic characterization of the [Ag₄₀(DMBT)₂₄(PPh₃)₈H₁₂]²⁺ (Ag₄₀H₁₂) cluster (DMBT = 2,4-dimethylbenzenethiol). The metal framework consists of three concentric shells of Ag₈@Ag₂₄@Ag₈, which can be described as (ν₁-cube)@(truncated-ν₃-octahedron)@(ν₂-cube), respectively. The presence of 12 hydrides in each cluster was systematically identified by various techniques. Based on a detailed analysis of the structural features and ¹H and ²H NMR spectra, the positions of the 12 hydrides were determined to be residing on the 12 edges of the cubic core. As a result, the electron count of the Ag₄₀ cluster is a two-electron superatomic system instead of a 14-electron system. Moreover, based on our DFT calculations and experimental probes, it was demonstrated that the 12 hydrides play a crucial role in stabilizing both the electronic and geometric structure of the Ag₄₀H₁₂ cluster. The successful synthesis of stable hydride-containing Ag nanoclusters and the identification of hydride positions are expected to simulate research attention on both synthesis and application of hydride-containing Ag nanomaterials.