Electronic state modulation of Ag₃₀ nanoclusters within a ring-shaped polyoxometalate

Atomically precise Ag nanoclusters display distinctive properties that are dictated by their structures and electronic states. However, manipulating the electronic states of Ag nanoclusters is challenging owing to their inherent instability and susceptibility to undesired structural changes, decomposition, and aggregation. Recently, we reported the synthesis of a body-centered cubic {Ag₃₀}²²⁺ nanocluster encapsulated within a ring-shaped polyoxometalate (POM) [P₈W₄₈O₁₈₄]^40- by reacting 16 Ag⁺-containing [P₈W₄₈O₁₈₄]^40- with Ag⁺ using N,N-dimethylformamide (DMF) as a mild reducing agent. This led to a redox-induced structural transformation into a face-centered cubic {Ag₃₀}¹⁶⁺ nanocluster. In this study, we demonstrated the modulation of the electronic states of Ag₃₀ nanoclusters within the ring-shaped POM through two different approaches. A face-centered cubic {Ag₃₀}¹⁸⁺ nanocluster, featuring distinct oxidation states compared to previously reported {Ag₃₀}²²⁺ and {Ag₃₀}¹⁶⁺ nanoclusters, was synthesized using tetra-n-butylammonium borohydride, a stronger reducing agent than DMF, in the reaction of 16 Ag⁺-containing [P₈W₄₈O₁₈₄]^40- and Ag⁺. Additionally, by leveraging the acid-base properties of POMs, we demonstrated the reversible, stepwise modulation of the charge distribution in the Ag₃₀ nanocluster through controlling protonation states of the ring-shaped POM ligand. These results highlight the potential of engineering POM-stabilized Ag nanoclusters with diverse structures and electronic states, thereby facilitating the exploration of novel properties and applications utilizing the unique characteristics of the POM ligands.