NHC-Stabilized Au Nanoclusters and Their Conversion to Au Nanoclusters.

Herein, we describe the synthesis of a toroidal Au cluster stabilized by -heterocyclic carbene and halide ligands reduction of the corresponding NHC-Au-X complexes (X = Cl, Br, I). The significant effect of the halide ligands on the formation, stability, and further conversions of these clusters is presented. While solutions of the chloride derivatives of Au show no change even upon heating, the bromide derivative readily undergoes conversion to form a biicosahedral Au cluster at room temperature. For the iodide derivative, the formation of a significant amount of Au was observed even upon the reduction of NHC-Au-I. The isolated bromide derivative of the Au cluster displays a relatively high (. 15%) photoluminescence quantum yield, attributed to the high rigidity of the cluster, which is enforced by multiple CH-π interactions within the molecular structure. Density functional theory computations are used to characterize the electronic structure and optical absorption of the Au cluster. C-Labeling is employed to assist with characterization of the products and to observe their conversions by NMR spectroscopy.