A series of POM-based compounds by tuning coordination groups and spacers of ligands: electrocatalytic, capacitive and photoelectrocatalytic properties

Abstract

Seven polyoxometalate-based compounds were synthesized under hydrothermal conditions, namely [Co(H₂Ptep)(HPtep)(H₂O)₂(PW₁₁CoO₃₉)]·4.5H₂O (1), {[Cu(H₃Ptep)₂(H₂Ptep)₂][SiW₁₂O₄₀]}·(SiW₁₂O₄₀)₂·8H₂O (2), {Cu₃(H₂Ptpi)₂(Ptpi)₂(H₂O)₅[(PMo₁₁CuO₃₉)₂]}·6H₂O (3), [Co(H₂Ptpi)₂(HPtpi)₂(SiMo₁₂O₄₀)₂]·2H₂O (4), [Co₃(Ptpi)₂(H₂O)₆(TeMo₆O₂₄)]·2H₂O (5), [Co₂Na(HPtpi)(H₂O)_7.5(TeMo₆O₂₄)]·3.5H₂O (6), [Cu(HZtpi)(H₂O)₂(CrMo₆(OH)₆O₁₈)]·5H₂O (7) (Ptep = 1-[2-(3-pyridin-4-yl-[1,2,4]triazol-4-yl)-ethyl]-piperazine, Ptpi = 1-[2-(3-pyridin-4-yl-[1,2,4]triazol-4-yl)-propyl]-imidazol, Ztpi = 1-[2-(3-pyrazin-4-yl-[1,2,4]triazol-4-yl)-propyl]-imidazol). Compounds 1–4 are all based on Keggin anions, especially 1 and 3 containing TMs monosubstituted Keggin anions. Compounds 5–7 are all based on Anderson anions. Compounds 1–4, 6 and 7 exhibit 0D, 1D and 2D structures, while compound 5 has a 3D structural framework. These seven compounds have excellent electrochemical properties and can be used as sensors for the amperometric detection of Cr(VI) and NO₂⁻. Among them, 1 and 4 possess favorable capacitance performance. Furthermore, compounds 3 and 4 have photoelectrocatalytic properties and can be used for the photoelectrocatalytic degradation of organic dye MB.