Probing the electronic structure and chemical bonding of the “staple” motifs of thiolate gold nanoparticles: Au(SCH3)2− and Au2(SCH3)3−

Abstract

Thiolate-protected gold nanoparticles have been found recently to be coordinated by the so-called “staple” bonding motifs, consisting of quasi-linear [RS–Au–SR] and V-shaped [RS–Au–(SR)–Au–SR] units, which carry a negative charge formally. Using photoelectron spectroscopy (PES) in conjunction with ab initio calculations, we have investigated the electronic structure and chemical bonding of the simplest staples with R = CH₃: Au(SCH₃)₂⁻ and Au₂(SCH₃)₃⁻, which were produced by electrospray ionization. PES data of the two Au–thiolate complexes are obtained both at room temperature (RT) and 20 K. The temperature-dependent study reveals significant spectral broadening at RT, in agreement with theoretical predictions of multiple conformations due to the different orientations of the –SCH₃ groups. The Au–S bonds in Au_n(SCH₃)_n+1⁻ (n = 1, 2) are shown to be covalent via a variety of chemical bonding analyses. The strong Au–thiolate bonding and the stability of the Au–thiolate complexes are consistent with their ubiquity as staples for gold nanoparticles and on gold surfaces.