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

Abstract

Silver nanoclusters (NCs) are of significant interest owing to their interesting structural, electronic, and catalytic properties. Among these NCs, Ag25(SR)18 is particularly attractive due to its identical geometry as its Au counterpart, Au25(SR)18. Herein, we present the site-specific electronic properties of Ag25(SR)18 and Au25(SR)18 using X-ray spectroscopy experiments and quantum simulations. To overcome the final state effect observed in X-ray photoelectron spectroscopy (XPS), a unique method was developed to reliably analyze the charge transfer behavior of the NCs. Density functional theory calculations were 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 were further compared and interpreted using the relativistic effect. The first derivative of the X-ray absorption near-edge structure (XANES) spectrum was further used as a tool to sensitively probe the bonding properties of Ag25(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 was demonstrated. These findings highlight the unique electronic properties of each atomic site in Ag25(SR)18; the effective X-ray analysis techniques developed here can offer new opportunities for the sitespecific study of other NCs.

Atom-precise silver–palladium bimetallic clusters on carbon supports as selective hydrogenation catalysts

“…15 In both systems, the Ag atom in the center position is most metallic with oxidation state of 0, the Ag atoms in surface position have oxidation states between 0 and +1 to suggest a mixture of both non-metallic and metallic natures, while the Ag atoms at the staple sites are in +1 oxidation state. 40 The Pd 3d 5/2 peak at 337.3 eV for the Ag 24 -Pd 1 clusters is consistent with a Pd(II) oxidation state in a thiolate environment. 41 The Ag 24 Pd 1 clusters have S 2p 3/2 peaks at 162.7 eV and 162.3 eV which suggests two metalthiolate (i.e.…”

“…S1 † shows the spectra and fitting results. For the Ag 3d peaks, the peak area ratio was constrained to 1 : ∼12 : ∼12 for Ag center : Ag surface : Ag staple to show the site-specific speciation of Ag atoms as described by Chen et al 40 Fig. S1(a) † shows a representative crystal structure of a 25 atom metal cluster which identifies the center atom, surface, and staple components.…”

Structural Analysis of Single-Atom Catalysts by X-ray Absorption Spectroscopy

“…In a typical XAS spectrum, there are two regions: the X-ray absorption near-edge structure (XANES) and the extended X-ray absorption fine structure (EXAFS), as shown in Figure . The XANES region usually reveals the electronic properties of materials such as oxidation states and d-electron density. , In addition, it can also serve as a fingerprint to probe the structures of materials, as different atomic arrangements and symmetries can produce different spectral features in the XANES region. The EXAFS region requires data analysis to uncover structural information such as coordination numbers (CNs), which is the number of neighboring atoms next to a chosen atom, bond distances, and Debye–Waller factors (σ 2 ).…”

Utilizing an Improved EXAFS Structure Analysis Method to Reveal Site-Specific Bonding Properties of Ag44(SR)30 Nanoclusters

“…X-ray absorption spectroscopy (XAS) is a powerful technique to study both electronic properties and bonding properties within one spectrum . The X-ray absorption near edge structure (XANES) has been successfully applied to investigate the electronic properties of NCs. − The extended X-ray absorption fine structure (EXAFS) is the region of XAS about 50 eV above the edge, which is useful for investigating the element-specific local structural environment of thiolate protected NCs under different conditions. − It has already been applied to study temperature effect on 25-atom NCs. , Generally, a thiolate protected NC has several different coordination environments, and the bond distances can be grouped into distinct shells. One major advantage of EXAFS is that it allows the observation of bond distance changes for each shell.…”