Gas-Phase Structures of [Au₂₁(SR)₁₄]⁻ and [Au₁₇(SR)₁₀]⁻ with Eight Electrons: Can They Support an Icosahedral Au₁₃ Core?

Abstract

A prototypical thiolate (RS)-protected gold cluster [Au 25 (SR) 18 ] − has high stability due to specific geometric and electronic structures: an icosahedral (I h ) Au 13 core with a closed electronic shell containing eight electrons is completely protected by six units of Au 2 (SR) 3 . Nevertheless, collisional excitation of [Au 25 (SR) 18 ] − in a vacuum induces the sequential release of Au 4 (SR) 4 to form [Au 21 (SR) 14 ] − and [Au 17 (SR) 10 ] − both containing eight electrons. To answer a naive question of whether these fragments bear an I h Au 13 (8e) core, the geometrical structures of [Au 21 (SC 3 H 7 ) 14 ] − and [Au 17 (SC 3 H 7 ) 10 ] − in the gas phase were examined by the combination of anion photoelectron spectroscopy and density functional theory (DFT) calculation of simplified models of [Au 21 (SCH 3 ) 14 ] − and [Au 17 (SCH 3 ) 10 ] − . We concluded that [Au 21 (SC 3 H 7 ) 14 ] − retains a slightly distorted I h Au 13 (8e) core, while [Au 17 (SC 3 H 7 ) 10 ] − has an amorphous Au 13 core composed of triangular Au 3 , tetrahedral Au 4 , and prolate Au 7 units. DFT calculations on putative species [Au 19 (SCH 3 ) 12 ] − and [Au 18 (SCH 3 ) 11 ] − suggested that the I h Au 13 (8e) core undergoes dramatic structural deformation due to mechanical stress from μ 2 ligation of only one RS.