On the Structure of Thiolate-Protected Au₂₅

Density functional theory is used to explore the structure of Au₂₅(RS)₁₈. The preferred structure consists of an icosahedral Au₁₃ core protected by 6 RS−Au−RS−Au−RS units. The enhanced stability of the structure as an anion is found to originate from closure of an eight-electron shell for delocalized Au(6s) electrons. The evaluated XRD pattern and optical spectra are in good agreement with experimental data.