Site-Specific and Size-Dependent Bonding of Compositionally Precise Gold−Thiolate Nanoparticles from X-ray Spectroscopy

Understanding the site-specific and size-dependent structure and bonding properties of gold−thiolate nanoparticles is one of the most fundamental questions in nanoscience. The recent synthesis of compositionally precise Aum(SR)n nanoparticles offers a promising opportunity to explicitly elucidate the structure−property correlation of nanomaterials from site-specific and size-dependent perspectives. Herein, we report an X-ray absorption (gold L3-, sulfur K-, and L3,2-edge) and photoemission (gold 4f, sulfur 2p, and valence band) study of compositionally precise Aum(SR)n nanoparticles. An X-ray spectroscopy approach to deduce the atomic structure of Au144(SR)60 is first demonstrated. In conjunction with ab initio calculations, a high-precision, atomic-site-specific illustration of the bonding in Au144(SR)60 is achieved. By comparing size-varied samples Au144(SR)60, Au38(SR)24, and Au25(SR)18, the size-dependent nature of bonding in gold−thiolate nanoparticles is revealed from both the sulfur and gold perspective.