Dynamic Balance between Heptamolybdate and Octamolybdate: Controlled Syntheses of Ag46 and Ag48 Nanoclusters and Their Transformation via pH-Regulated Ligand Exchange

The integration of polyoxometalates (POMs) as structural templates for noble metal nanoclusters (NCs) represents a cutting-edge strategy to achieve atomic-level precision in cluster synthesis, but the relationship between polyoxometalates and overall structures of assembled NCs and their transformations often are not clear due to significant complexity coming from transient intermediates and coexisting species. Herein, we report the trifluoroacetic acid (TFA)-mediated controlled syntheses and pH-regulated induced structural transformation of silver NCs: [(Mo7O24)@Ag46(CyhS)28(CF3COO)10(CH3CN)4]•2COOCF3–•2CH3CN and [(Mo8O28)@Ag48(CyhS)24(CF3COO)16(CH3CN)4]•7.5CF3COOH (abbreviated as Ag46 and Ag48). Both clusters feature core–shell architectures with molybdenum-based POMs ([Mo7O24]6– and [Mo8O28]8–) acting as anionic templates directing the assembly of Ag shells. The structural evolution from Ag46 to Ag48 was achieved via pH-regulated ligand exchange, highlighting the dynamic balance between POM cores of different sizes, Ag shell coordination geometry, and TFA’s dual role. This work advances the frontier of hybrid NC-POM systems, offering insights into cluster transformation mechanisms and programmable synthesis.