Tuning the Magic Sizes and Optical Properties of Atomically Precise Bidentate N‐Heterocyclic Carbene‐Protected Gold Nanoclusters via Subtle Change of N‐Substituents

Abstract Owing to the atomically precise structures, metal nanoclusters (NCs) have always served as model molecular tools to analyze NC surface chemistry and to investigate structure−property correlations. Herein, a series of bis‐N‐heterocyclic carbene (NHC)‐protected NCs of type [Au₁₁(bis‐NHC)₅]³⁺ and [Au₁₃(bis‐NHC)₅Br₂]³⁺ obtained from direct reduction of Au−bis‐NHC complexes are described. The NCs type obtained depends on the N‐wingtip substituents of the Au−bis‐NHC complexes. Subtle changes in the lengths of the N‐wingtip substituents enable the fine‐tuning of the kernel with either Au₁₁ or Au₁₃ clusters. Among them, [Au₁₁(bis‐NHC)₅]³⁺ cluster is the first homoleptic NHC‐stabilized Au NC. The composition and structures of these NCs are unequivocally determined by single crystal X‐ray crystallography and electrospray ionization mass spectrometry. Contrary to the non‐emissive Au₁₁ cluster, the Au₁₃ NC exhibits high emission in solution and the luminescence properties are severely dependent onto the substituent effects. Additionally, peculiar Au⋯HC interactions are present in NHC‐protected clusters.