Polyoxovanadate Building Units in Metal–Organic Frameworks: Coordination Connectivity and Selective Oxidation of Aromatic Thioether

Polyoxovanadate (POV) clusters, with their diverse vanadium-oxo coordination modes, provide structurally well-defined inorganic nodes for constructing functional metal-organic frameworks (MOFs). In this work, four polyoxovanadate-based metal-organic frameworks [Co₂(DPP)₄(V₄O₁₂)]·0.25H₂O (1), [M₃(DPP)₄(H₂O)₄(V₆O₁₈)]·2H₂O (M = Co (2) and Ni (3)), and [Zn₃(DPP)₃(V₆O₁₈)] (4) (DPP = 1,3-Di(4-pyridyl)propane) were reported and structurally characterized by single-crystal X-ray diffraction. These materials feature distinct POV motifs, including cyclic {V₄} units and extended {V₃}/{V₆} vanadium-oxo chains, providing well-defined coordination environments around the metal nodes. All four MOFs efficiently catalyzed the oxidation of aromatic thioethers using H₂O₂ with high selectivity for sulfoxide formation. Among them, compound 4 exhibited the highest activity and excellent recyclability over at least five cycles, consistent with its robust structural stability. Comparative catalytic and structural analyses suggest that the superior performance of 4 originates from the parallel and independent action of unsaturated V and Zn centers within its zigzag V-Zn chains. This study demonstrates that tuning POV building units and their coordination connectivity provides an effective strategy for controlling activity and selectivity in oxidation reactions.