An Imidazole-Functionalized Polyoxovanadate with a Classical {V₁₈O₄₂} Core and Its Photothermal Conversion Behavior

The classical {V₁₈O₄₂} cage is a cornerstone of the polyoxovanadate (POV) family, distinguished by its tunable V(IV)/V(V) ratio and its ability to generate diverse derivatives through semimetal-ion incorporation. However, structurally well-defined organic functionalization of the {V₁₈O₄₂} cage remains largely unexplored. In this work, an imidazole-functionalized mixed-valence POV featuring a {V₁₈O₄₂} core, H[(VO)(mIM)₄]₄[V₁₈O₄₂(Cl)]·13H₂O (V₂₂-mIM), was synthesized and structurally characterized. Single-crystal X-ray diffraction reveals that V₂₂-mIM consists of a classical {V₁₈O₄₂} cluster constructed exclusively from square-pyramidal {VO₅} units and capped by four vanadium centers coordinated by nitrogen-donor ligands, affording the first example of an organic functionalized {V₁₈O₄₂} cage. Bond valence sum and X-ray photoelectron spectroscopy confirm the mixed-valence nature of the cluster, consisting of 18 V(IV) and 4 V(V) centers. Consistent with intervalence charge-transfer transitions within the mixed-valence POV skeleton, V₂₂-mIM displays broad visible-light absorption and exhibits pronounced photothermal conversion behavior under 660 nm irradiation in both solution and the solid state, together with reproducible cycling stability. This study expands the structural chemistry of POVs and demonstrates that well-defined mixed-valence POVs can serve as molecular platforms for photothermal conversion.