Solvent-mediated precipitating synthesis and optical properties of polyhydrido Cu nanoclusters with four vertex-sharing tetrahedrons.

Structurally defined metal nanoclusters facilitate mechanism studies and promote functional applications. However, precisely constructing copper nanoclusters remains a long-standing challenge in nanoscience. Developing new efficient synthetic strategies for Cu nanoclusters is highly desirable. Here, we propose a solvent-mediated precipitating synthesis (SMPS) to prepare CuH(SR)(PPh) nanoclusters (H-SR = 2-chloro-4-fluorobenzenethiol). The obtained Cu nanoclusters are high purity and high yield (39.5%, based on Cu atom), proving the superiority of the SMPS method. The Cu nanoclusters were comprehensively studied a series of characterizations. Single crystal X-ray crystallography shows that the Cu nanoclusters contain a threefold symmetry axis and the Cu kernel is protected by a monolayer of ligands, including PPh and thiolates. Unprecedentedly, the aesthetic Cu kernel is composed of four vertex-sharing tetrahedrons, rather than the common icosahedral or cuboctahedral M. The intramolecular π⋯π interactions between thiolates and PPh on the surface contribute to the stable configuration. Furthermore, electrospray ionization mass spectrometry (ESI-MS) and nuclear magnetic resonance (NMR) revealed the existence of ten hydrides, including four types of hydrides. Density functional theory (DFT) calculations without simplifying the ligands simulated the location of the 10 hydrides in the crystal structure. Additionally, the steady-state ultraviolet-visible absorption and fluorescence spectra of the Cu nanoclusters exhibit unique optical absorbance and photoluminescence. The ultrafast relaxation dynamics were also studied transient absorption spectroscopy, and the three decay components are attributed to the relaxation pathways of internal conversion, structural relaxation and radiative relaxation. This work provides not only a novel SMPS strategy to efficiently synthesize Cu nanoclusters, but also a better insight into the structural characteristics and optical properties of the Cu nanoclusters.