文摘
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-rayabsorption spectroscopy. The number of gold atoms in the cores of these two clusters was determinedquantitatively 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 Aumetal cores of each of these complexes adopt an icosahedral structure with a relaxation of the icosahedralstrain. Data from microscopy and spectroscopy studies extended to larger thiolate-protected gold clustersshowing 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 thiolateligands bond preferentially at 3-fold atomic sites on the nanoparticle surface, establishing an averagecomposition 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 previousreports that were interpreted as indicating Au MPC structures consisting of a Au core, Au2S shell, and thiolatemonolayer.