Bimetallic Ag125Cu8 Nanocluster, Structure Determination, and Nonlinear Optical Properties

The atomic precision of the subnanometer nanoclusters has provided sound proof on the structural correlation of metal complexes and larger-sized metal nanoparticles. Herein, we report the synthesis, crystallography, structural characterization, electrochemistry, and optical properties of a 133-atom intermetallic nanocluster protected by 57 thiolates (3-methylbenzenethiol, abbreviated as m -MBTH) and 3 chlorides, with the formula of Ag 125 Cu 8 ( m -MBT) 57 Cl 3 . This is the largest Ag–Cu bimetallic cluster ever reported. Crystallographic analysis revealed that the nanocluster has a three-layer concentric core–shell structure, Ag 7 @Ag 47 @Ag 71 Cu 8 S 57 Cl 3, and the Ag 54 metal kernel adopts a D 5 h symmetry. The nuclei number is between that of the previously reported large silver cluster [Ag 136 (SR) 64 Cl 3 Ag 0.45 ] − and the large silver-rich cluster Au 130– x Ag x (SR) 55 ( x = 98). All these three clusters bear a similar metallic core structure, while the main structural difference lies in the shell motif structures. Electron counting revealed an open electron shell with 73 delocalized electrons, which was verified by the electron paramagnetic resonance analysis. The DPV electrochemical measurement indicates a multielectron state quantization double-layer charging shape and single-electron sequential charging and discharging characteristic of the AgCu alloy cluster. In addition, the open-hole Z-scan test reveals the nonlinear optical absorption (2–3 optical absorption in the NIR-II/III region) of Ag 125 Cu 8 nanoclusters.