NHC-Stabilized Au10 Nanoclusters and Their Conversion to Au25 Nanoclusters

Herein, we describe the synthesis of a toroidal Au-10 cluster stabilized by N-heterocyclic carbene and halide Iigands via 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-10 show no change even upon heating, the bromide derivative readily undergoes conversion to form a biicosahedral Au-25 cluster at room temperature. For the iodide derivative, the formation of a significant amount of Au-25 was observed even upon the reduction of NHC-Au-I. The isolated bromide derivative of the Au-25 cluster displays a relatively high (ca. 15%) photoluminescence quantum yield, attributed to the high rigidity of the duster, which is enforced by multiple CH-pi interactions within the molecular structure. Density functional theory computations are used to characterize the electronic structure and optical absorption of the Au-10 cluster. C-13-Labeling is employed to assist with characterization of the products and to observe their conversions by NMR spectroscopy.

Automated summary

The synthesis of a toroidal Au-10 cluster stabilized by N-heterocyclic carbene and halide ligands is described via reduction of NHC-Au-X complexes (X = Cl, Br, I). The halide ligands significantly affect the formation, stability, and conversions of these clusters. The bromide derivative readily converts to a biicosahedral Au-25 cluster at room temperature, while the iodide derivative shows significant formation of Au-25 upon reduction of NHC-Au-I. The isolated bromide derivative of Au-25 cluster exhibits relatively high photoluminescence quantum yield due to the high rigidity enforced by multiple CH-pi interactions.