Polyoxometalate-based CuII/CoII complexes tuned using various metal–pyrazole loops: design, diverse architectures and catalytic activity toward the oxidation of thioether derivatives

Abstract

In the presence of the ligand N,N-bis(3-pyrazolamide)-1,2-hexahydrobenzene (H₂dpyh), three diverse fascinating structures were constructed from different polyoxometalate (POM) anions and Cu^II/Co^II ions: {Cu₈(μ₂-OH)₂(dpyh)₄[CrMo₆(OH)₅O₁₉](H₂O)₈}·2[CrMo₆(OH)₆O₁₈]·4H₂O (1), {Co(H₂dpyh)[β-Mo₈O₂₆]_0.5(H₂O)} (2) and {Co₃(H₂dpyh)₂[TeMo₆O₂₄](H₂O)₆} (3). Complexes 1–3 were characterized through single crystal X-ray diffraction, IR spectra and powder X-ray diffraction. Single-crystal analysis shows that complexes 1–3 contain internal flexible metal–pyrazole loops and different POMs, which exhibit 1D chain or 2D layer networks, respectively. Directed by the coordination modes of the POM anions and central metals, the shape and size of these metal–pyrazole loops can be tuned, which further influence the final structures and catalytic properties of complexes 1–3. The catalytic activity of these POM-based complexes toward the oxidation of thioether derivatives has been investigated, which proved the effect of metal–pyrazole loops and their final structures on the catalysis of the title complexes as heterogeneous catalysts.