New pyrimidine-amide-tetrazole ligand derived polyoxometalate-based copper complexes as catalysts for sulfide-sulfoxide transformation and electrochemical sensors

Abstract

In this study, a new ligand, 5-(4-pyrimidinecarboxamido)-1H-tetrazol (4-H₂pat), was synthesized by connecting the pyrimidine group and tetrazole group through an amide bond for the first time, aiming to construct new POM-based metal–organic complexes (POMOCs). By using the ligand 4-H₂pat, two new POMOCs, [Cu₄(4-pat)₂(μ₂-OH)(CrMo₆(OH)₆O₁₈)(H₂O)₃]·2H₂O (1) and [Cu₂(4-pat)(β-Mo₈O₂₆)_0.5(H₂O)₃] (2), were successfully synthesized under solvothermal and hydrothermal conditions, respectively. The structures were characterized by single crystal X-ray diffraction analysis, IR spectroscopy and powder X-ray diffraction (PXRD). In complex 1, the 1D [Cu₄(μ₂-OH)(4-pat)₂]_n³ⁿ⁺ metal–organic chains were connected by μ₂-bridging [CrMo₆(OH)₆O₁₈]³⁻ (CrMo₆) anions to construct a 2D layered structure. In complex 2, the 2D [Cu₂(4-pat)]_n²ⁿ⁺ metal–organic grid framework was consolidated by the μ₄-bridging [β-Mo₈O₂₆]⁴⁻ (Mo₈) anions. The use of two different POM anion clusters results in the formation of two diverse 2D framework structures. Complexes 1 and 2 can effectively catalyze the oxidation of methyl phenyl sulfide as non-homogeneous catalysts with 97% and 95% conversions, respectively. They can also be used as electrocatalysts to prepare bulk-modified electrodes for detecting Cr(VI) and Fe(III) ions with low detection limits. In addition, the effects of different POMs on the structures and catalytic/electrocatalytic performances of the title complexes were discussed.