Geometric Nonuniformity Localizes Valence Orbitals in Gold Clusters: Case Study on [Au ₂₃ (SC ₆ H ₁₁ ) ₁₆ ] ^–

ABSTRACT To elucidate the effect of geometric nonuniformity on electronic structures of monolayer‐protected gold clusters, the valence orbitals of [Au 23 (SC 6 H 11 ) 16 ] – ( Au 23 − ), which features a nonuniform Au 13 core, were investigated by using anion photoelectron spectroscopy and density functional theory calculations. The energy levels of the valence orbitals of Au 23 − were more appropriately described by a model comprising 1S orbitals localized on Au 3 or Au 4 units within the Au 13 core, rather than by the deformed jellium model. Meanwhile, the calculated valence orbitals of a hypothetical [Au 23 (SC 6 H 11 ) 16 ] – cluster with a uniform Au 13 core were better described by the jellium model, suggesting that the geometric nonuniformity of the Au 13 core is the direct cause of electronic localization in Au 23 − . The localized nature of the molecular orbitals involved in photoabsorption accounts for the significantly larger molar absorption coefficient of Au 23 − compared to those of typical Au 13 superatoms with uniform structures.