Metal Core Bonding Motifs of Monodisperse Icosahedral Au₁₃ and Larger Au Monolayer-Protected Clusters As Revealed by X-ray Absorption Spectroscopy and Transmission Electron Microscopy

Abstract

The atomic metal core structures of the subnanometer clusters Au13[PPh3]4[S(CH2)11CH3]2Cl2 (1) and Au13[PPh3]4[S(CH2)11CH3]4 (2) were characterized using advanced methods of electron microscopy and X-ray absorption spectroscopy. The number of gold atoms in the cores of these two clusters was determined quantitatively using high-angle annular dark field scanning transmission electron microscopy. Multiple-scattering-path analyses of extended X-ray absorption fine structure (EXAFS) spectra suggest that the Au metal cores of each of these complexes adopt an icosahedral structure with a relaxation of the icosahedral strain. Data from microscopy and spectroscopy studies extended to larger thiolate-protected gold clusters showing a broader distribution in nanoparticle core sizes (183 +/- 116 Au atoms) reveal a bulklike fcc structure. These results further support a model for the monolayer-protected clusters (MPCs) in which the thiolate ligands bond preferentially at 3-fold atomic sites on the nanoparticle surface, establishing an average composition for the MPC of Au180[S(CH2)11CH3]40. Results from EXAFS measurements of a gold(I) dodecanethiolate polymer are presented that offer an alternative explanation for observations in previous reports that were interpreted as indicating Au MPC structures consisting of a Au core, Au2S shell, and thiolate monolayer.

Electronic structure, magnetic properties, and microstructural analysis of thiol-functionalized Au nanoparticles: role of chemical and structural parameters in the ferromagnetic behaviour

“…4a), which suggests that this sample has a polymeric-like electronic structure; this is the electronic structure that would correspond to a polymeric precursor, as it has been previously described in previous publications (Menard et al, 2006;Guerrero et al, 2007). The gold found in the polymeric precursor happens to have an electronic behaviour far-off from the one of bulk gold, instead, the electronic properties of the polymeric precursor and the commercial gold sulphide are alike: the large number of gold atoms bonded to sulphur leads to a maximum value of the d-hole density in the Au atom.…”

“…This means that the investigated NPs have a crystalline fcc structure similar to bulk gold (c.f. Menard et al, 2006). Then, it could be said that any change in the white line intensity should be due to a charge transfer phenomenon between gold and sulphur, as Zhang and Sham (2003) have previously reported .…”

Bonding properties of thiolate-protected gold nanoclusters and structural analogs from X-ray absorption spectroscopy

“…This provides a qualitative view of the local structure environment around the absorbing atom without fitting the EXAFS data. Although it is possible to obtain structural details of the sample by fitting longer-range single scattering or multiple scattering features in the EXAFS spectrum [37], this can be difficult for Au NC samples due to the small particle size and short-range order. In this review, single scattering shells are mainly interpreted for various metal-ligand and metalmetal scattering paths.…”

Statistical analysis of support thickness and particle size effects in HRTEM imaging of metal nanoparticles

“…Supplemental Materials S2 is a representative HRTEM image showing the size range of the resulting Au NPs. Based on the range of observed NP sizes and previous studies of Au NP [13,24], it was assumed that all the examined NP were crystalline. TEM characterization was carried-out using a Philips CM300 FEG TEM/STEM (Cs ¼ 0.65 mm) and the double-aberration-corrected FEI TEAM 0.5 TEM/STEM (Cs ¼ 0.005 mm), both with UltraTwin pole pieces and operated at 300 kV without monochromation to ensure comparable information limits (0.8 Å).…”

“…Au nanoparticles were selected as -based on previous work in Ref. [13,24] and the sizes of nanoparticles measured in this study -it is reasonable to assume all the examined nanoparticles were crystalline and that lack of lattice fringe visibility was due entirely to imaging limitations rather than changes in nanoparticle morphology. Additionally, Au nanoparticles do not oxidize upon exposure to air, avoiding structural changes that would have complicated the analysis.…”