Gas-Phase Structures of [Au(SR)] and [Au(SR)] with Eight Electrons: Can They Support an Icosahedral Au Core?

A prototypical thiolate (RS)-protected gold cluster [Au(SR)] has high stability due to specific geometric and electronic structures: an icosahedral () Au core with a closed electronic shell containing eight electrons is completely protected by six units of Au(SR). Nevertheless, collisional excitation of [Au(SR)] in a vacuum induces the sequential release of Au(SR) to form [Au(SR)] and [Au(SR)] both containing eight electrons. To answer a naive question of whether these fragments bear an Au(8e) core, the geometrical structures of [Au(SCH)] and [Au(SCH)] in the gas phase were examined by the combination of anion photoelectron spectroscopy and density functional theory (DFT) calculation of simplified models of [Au(SCH)] and [Au(SCH)]. We concluded that [Au(SCH)] retains a slightly distorted Au(8e) core, while [Au(SCH)] has an amorphous Au core composed of triangular Au, tetrahedral Au, and prolate Au units. DFT calculations on putative species [Au(SCH)] and [Au(SCH)] suggested that the Au(8e) core undergoes dramatic structural deformation due to mechanical stress from μ ligation of only one RS.