Structural and Chemical Bonding Properties of AuSH: A Photoelectron Velocity-Map Imaging Spectroscopic and Theoretical Study.

Mass-selected photoelectron velocity-map imaging spectroscopy was employed to investigate the geometrical and electronic properties of AuSH. The comprehensive comparison between the experiment and theoretical calculations establishes that the ground-state AuSH anion has a mixed-ligand structure [SAuSH] with an unsymmetrical S-Au-S unit. Further chemical bonding analyses on AuSH and comparison with the isoelectronic AuS suggest that the unique S-Au-S unit in these species features two three-center, three-electron π-bonding, and one three-center, two-electron σ-bonding. The isoelectronic replacement of the extra electron in AuS by the H atom can lead to σ bonding evolution from the electron-sharing bond to the dative bond. These findings are conducive to the fundamental understanding of the intrinsic stability of thiolate-protected gold nanoclusters and their delicate ligand design to achieve desirable properties.