Insights into the Metal-Exchange Synthesis of MAg₂₄(SR)₁₈(M = Ni, Pd, Pt) Nanoclusters

The metal-exchange reaction is a powerful means to generate atomically precise alloy nanoclusters. Both galvanic and antigalvanic exchange strategies have been devised to produce various doped metal nanoclusters with atomic precision. Here we report new insights into the metal-exchange synthesis of MAg24(SPhMe2)18 (M = Ni, Pd, Pt) nanoclusters. Based on the redox potential comparison of the Ag25 template with metal ion dopants, we reveal that the metal-exchange reaction is a redox potential-driven process and propose a two-step metal-exchange model that includes dopant deposition and host dissolution steps. With the help of a co-reductant and a counterion, the high-yield metal-exchange syntheses of MAg24(SPhMe2)18 nanoclusters are demonstrated, yielding center-doped [NiAg24(SPhMe2)18]0, [PdAg24(SPhMe2)18]2-, and [PtAg24(SPhMe2)18]2- nanoclusters in >70% yield. Voltammetric and density functional investigations reveal that [NiAg24(SPhMe2)18]0 is a six-electron superatom having a distorted core due to the Jahn-Teller effect. The neutral [NiAg24(SPhMe2)18]0 becomes an eight-electron [NiAg24(SPhMe2)18]2- superatom upon chemical reduction, which has an isotropic core as confirmed by single-crystal X-ray diffraction.