A series of POM compounds constructed using a flexible ligand containing three coordination groups: electrocatalytic and photocatalytic reduction and amperometric detection of Cr(vi)

Abstract

Four polyoxometalate-based compounds were synthesized by a hydrothermal method, namely [Ni₂(HPtpi)(H₂O)_7.5Mo_0.17(TeMo₆O₂₄)]·2.5H₂O (1), [Co(HPtpi)₂(H₂Ptpi)₂(GeMo₁₂O₄₀)₂]·4H₂O (2) and {[M(Ptpi)(H₂Ptpi)(H₂O)][(γ-Mo₈O₂₆)_0.5(α-Mo₈O₂₆)_0.5]}·4H₂O (M = Co in 3; Ni in 4) (Ptpi = 1-[2-(3-pyridin-4-yl-[1,2,4]triazol-4-yl)-propyl]-imidazol). Compound 1 exhibits a 3D structure with TeMo₆ anions linked by [Ni₂(Ptpi)]⁴⁺ subunits. Compound 2 possesses a dissociative anionic dimer linked by a [Co(Ptpi)₄]²⁺ subunit. Compounds 3 and 4 are isostructural, containing two kinds of [Mo₈O₂₆]⁴⁻ anions. The γ-Mo₈ anions connect metal–organic chains to form a 2D layer, while the α-Mo₈ anions disperse between two adjacent layers. Compounds 1–4 can be used as electrocatalysts for the electrocatalytic reduction of NO₂⁻, Cr(VI) and BrO₃⁻ as well as the electrocatalytic oxidation of ascorbic acid. Compounds 1–4 can also be used as electrochemical sensors for the amperometric detection of NO₂⁻ and Cr(VI), with good sensitivity and a wide concentration range. Compounds 1–4 also exhibit good performance for the photocatalytic reduction of Cr(VI), from which compound 3 has the best photocatalytic activity.