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 Ag₁₂₅Cu₈(m-MBT)₅₇Cl₃. This is the largest Ag-Cu bimetallic cluster ever reported. Crystallographic analysis revealed that the nanocluster has a three-layer concentric core-shell structure, Ag₇@Ag₄₇@Ag₇₁Cu₈S₅₇Cl₃, and the Ag₅₄ metal kernel adopts a D₅ symmetry. The nuclei number is between that of the previously reported large silver cluster [Ag₁₃₆(SR)₆₄Cl₃Ag_0.45]^- and the large silver-rich cluster Au_130-Ag(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 Ag₁₂₅Cu₈ nanoclusters.