Synthesis, structures and catalytic properties of two organic–inorganic hybrid polyoxometalates built from {Ni6PW9} units

Abstract

Two new Ni₆-added organic–inorganic hybrid polyoxometalates, {[Ni(en)₂][Ni₆(μ₃-OH)₃(H₂O)₃(Hen)(en)₃(3,5-DDB)(B-α-PW₉O₃₄)][Ni₆(μ₃-OH)₃(H₂O)₂(en)₃(Ac)(3,5-DDB)(B-α-PW₉O₃₄)]}·8H₂O (1, en = ethylenediamine, 3,5-DDB = 3,5-dihydroxybenzoic acid) and [Ni(en)₂][Ni₆(μ₃-OH)₃(H₂O)₄(en)₂(5-HIP)(B-α-PW₉O₃₄)]·3H₂O (2, 5-HIP = 5-hydroxyisophthalic acid), were synthesized using a lacunary-directing synthetic strategy. 1 forms a novel dumbbell-shaped dimer structure consisting of two distinct Ni₆-added POMs linked by [Ni(en)₂]²⁺ cations. 2 exhibits a one-dimensional (1D) chain structure assembled from [Ni₆(μ₃-OH)₃(H₂O)₄(en)₂(B-α-PW₉O₃₄)]²⁻ structural building units bridged by 5-HIP ligands. Electrochemical studies revealed that 1 exhibits significant electrocatalytic activity for the reduction of H₂O₂ and NO₂⁻. Furthermore, evaluation experiments on oxidative desulfurization revealed that complex 2 exhibits a higher desulfurization conversion rate for dibenzothiophene (DBT) compared to complex 1. Additionally, it was observed that increasing both the reaction temperature and the amount of H₂O₂ further improved the desulfurization efficiency of DBT.