Gold–Thiolate Ring as a Protecting Motif in the Au₂₀(SR)₁₆ Nanocluster and Implications

Abstract

Understanding how gold nanoclusters nucleate from Au^ISR complexes necessitates the structural elucidation of nanoclusters with decreasing size. Toward this effort, we herein report the crystal structure of an ultrasmall nanocluster formulated as Au₂₀(TBBT)₁₆ (TBBT = SPh-<i>t</i>-Bu). The structure features a vertex-sharing bitetrahedral Au₇ kernel and an unprecedented “ring” motifAu₈(SR)₈. This large ring protects the Au₇ kernel through strong Au_ring–Au_kernel bonding but does not involve S–Au_kernel bonding, in contrast to the common “staple” motifs in which the S–Au_kernel bonding is dominant but the Au_staple–Au_kernel interaction is weak (i.e., aurophilic). As the smallest member in the TBBT “magic series”, Au₂₀(TBBT)₁₆, together with Au₂₈(TBBT)₂₀, Au₃₆(TBBT)₂₄, and Au₄₄(TBBT)₂₈, reveals remarkable size-growth patterns in both geometric structure and electronic nature. Moreover, Au₂₀(TBBT)₁₆, together with the Au₂₄(SR)₂₀ and Au₁₈(SR)₁₄ nanoclusters, forms a “4e” nanocluster family, which illustrates a trend of shrinkage of bitetrahedral kernels from Au₈⁴⁺ to Au₇³⁺ and possibly to Au₆²⁺ with decreasing size