Divide and Protect: Capping Gold Nanoclusters with Molecular Gold−Thiolate Rings

Abstract

Density functional theory calculations are used to explore phosphine- and thiolate-protected gold nanoclusters, namely, Au₃₉(PH₃)₁₄Cl₆ and Au₃₈(SCH₃)₂₄. For Au₃₈(SCH₃)₂₄, a novel structural motif is predicted, consisting of ringlike (AuSCH₃)₄ units protecting a central Au₁₄ core. The calculated optical spectrum of this species features a large optical gap (about 1.5 eV) and a prominently peaked structure, correlating with experimental findings of “molecular-like spectra” of thiolate-protected 1.1 nm gold nanoparticles. Ligand−ligand interactions and steric effects in the ligand shell are suggested as possible driving forces toward an ordered gold core structure. A novel mechanism for ligand-exchange reactions on gold clusters is proposed.