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

摘要

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 [Au-11(bis-NHC)(5)](3+) and [Au-13(bis-NHC)(5)Br-2](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 Au-11 or Au-13 clusters. Among them, [Au-11(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 Au-11 cluster, the Au-13 NC exhibits high emission in solution and the luminescence properties are severely dependent onto the substituent effects. Additionally, peculiar AuMIDLINE HORIZONTAL ELLIPSISH-C interactions are present in NHC-protected clusters.