Anderson-type polyoxometalate-based sandwich complexes bearing a new “V”-like bis-imidazole-bis-amide ligand as electrochemical sensors and catalysts for sulfide oxidation

By introducing a new “V”-like semirigid bis-imidazole-bis-amide ligand, 4,4’-bis(1H-imidazole-4-carboxamide)phenylmethane (L), into a reaction system containing Anderson-type polyoxoanions, three polyoxometalate-based metal–organic complexes (POMOCs) with different metal ions were successfully synthesized under solvothermal conditions. The as-prepared POMOCs [Zn₂L₂(H₂O)₄][Zn(H₂O)₂(TeMo₆O₂₄)]·9H₂O (1), [Ni(H₂O)₆][Ni₂L₂(H₂O)₂[AlMo₆(OH)₆O₁₈]₂]·9H₂O (2), and [Co(H₂O)₆][Co₂L₂(H₂O)₂[AlMo₆(OH)₆O₁₈]₂]·11.5H₂O (3) show sandwich-like supramolecular structures. Complexes 2 and 3 are isostructural, having two [ML(H₂O)₂]²⁺ chains with [AlMo₆(OH)₆O₁₈]³⁻ polyoxoanions as pendants arranged in an interdigital mode to construct the sandwich-like architecture, whereas in complex 1 the anionic [Zn(H₂O)₂(TeMo₆O₂₄)]⁴⁻ chain is sandwiched by two cationic [ZnL(H₂O)₂]²⁺ chains to generate the supramolecular structure. POMOCs 1–3 display excellent electrochemical sensing behavior for Cr(VI), Fe(III), BrO₃⁻, and NO₂⁻ ions and efficient catalytic performance in sulfide oxidation. The effect of the central metal on the electrochemical sensing and sulfide oxidation performance and that of the special architecture of 1 on the detection ability are discussed.