Different Anderson-type polyoxometalate-based metal–organic complexes exhibiting –OH group-directed structures and electrochemical sensing performance

Abstract

By regulating different metal ions and polyoxometalates (POMs), four Anderson-type POM-based metal-pyrazolamide complexes, namely, {M₂(L)₂ [XMo₆(OH)₅O₁₉](H₂O)₂} (M = Co, X = Cr (1), M = Ni, X = Al (2)) and {M₃(L)₂[XMo₆O₂₄](H₂O)₆} (X = Te, M = Co (3), M = Ni (4), (L = N,N-bis(3-pyrazolamide)-1,2-ethane)), were obtained under hydrothermal conditions. The results of characterization of IR spectra and powder X-ray diffraction patterns, as well as single-crystal X-ray diffraction analysis, are provided. Complexes 1 and 2 displayed isostructural 1D chains constructed from B-type [CrMo₆(OH)₅O₁₉]⁴⁻ anions and [M₂(L)₂]⁴⁺ loops. Complexes 3 and 4 exhibited 2D networks derived from A-type [TeMo₆O₂₄]⁶⁻ anions and [M₂(L)₂]⁴⁺ loops. The effects of the POM types on their structures and properties were investigated. Complexes 1–4 showed electrocatalytic performance for bromate reduction. Only complexes 1 and 2 constructed from B-type Anderson polyoxoanions showed electrocatalytic activity towards the oxidation of dopamine. It is notable that complex 3 after potentiostatic treatment also shows electrocatalytic activity towards the oxidation of dopamine, which indicates that the –OH from the Anderson-type POM played a vital role in the electrocatalytic oxidation of dopamine. All the title complexes showed adsorption activity for gentian violet, and complexes 3 and 4 exhibited better adsorption capacities for methylene blue than 1 and 2.