Site-Specific Electronic Properties of [Ag25(SR)18]- Nanoclusters by X-Ray Spectroscopy

Silver nanoclusters (NCs) are of significant interest owing to their interesting structural, electronic, and catalytic properties. Among these NCs, Ag-25(SR)(18) is particularly attractive due to its identical geometry as its Au counterpart, Au-25(SR)(18). Herein, the site-specific electronic properties of Ag-25(SR)(18) and Au-25(SR)(18) using X-ray spectroscopy experiments and quantum simulations are presented. To overcome the final state effect observed in X-ray photoelectron spectroscopy (XPS), a unique method is developed to reliably analyze the charge transfer behavior of the NCs. Density functional theory calculations are combined with XPS to provide more insight into the electronic properties of the NCs. The differences in the XPS valence bands of these two NCs are further compared and interpreted using the relativistic effect. The first derivative of the X-ray absorption near-edge structure (XANES) spectrum is further used as a tool to sensitively probe the bonding properties of Ag-25(SR)(18). By combining the experimental XANES data and their site-specific quantum simulations, the large impact of the staple motif on the bonding properties of the NC is demonstrated. These findings highlight the unique electronic properties of each atomic site in Ag-25(SR)(18); the effective X-ray analysis techniques developed here can offer new opportunities for the site-specific study of other NCs.