An Ultrastable, Small {Ag7}5+ Nanocluster within a Triangular Hollow Polyoxometalate Framework

Small Ag_n nanoclusters (n<10) have been emerging as promising materials as sensing, biolabeling, and catalysis because of their unique electronic states and optical properties. However, studying synthesis, structure determination, and exploration of their properties remain major challenges as a result of the low stability of small Ag nanoclusters. Herein, we synthesized an atomically precise face-centered-cubic-type small {Ag₇ }⁵⁺ nanocluster supported by a novel triangular hollow polyoxometalate (POM) framework [Si₃ W₂₇ O₉₆ ]^18- . The cluster showed unique {Ag₇ }⁵⁺ -to-POM charge transfer bands in both visible and UV light regions. Furthermore, this small {Ag₇ }⁵⁺ nanocluster exhibited an unprecedented ultrastability in solution, despite having exposed Ag sites that can be accessed by small molecules, such as O₂ , water, and solvents.