Synthesis and photo-/electro-catalytic properties of a 3D POMOF material based on an interpenetrated copper coordination polymer linked by in situ dual ligands and Dawson-type phosphotungstates

Abstract

A novel 3D polyoxometalate metal organic framework (POMOF), [{Cu^II₆Cu^I₁₀ (H₂O)₅(pzc)₁₀(pz)₆}{P₂W₁₈O₆₂}₂]·4H₂O (1) (Hpzc = pyrazine-2-carboxylic acid, pz = pyrazine) has been hydrothermally synthesized and characterized by IR, TG, XRD, UV-vis and elemental analyses. In compound 1, the pzc and pz ligands are generated through in situ transformation from pyrazine-2,3-dicarboxylic acid (pzdc) to remove one or two CO₂ molecules. The ligands with four coordination modes connect nine crystallographically independent Cu atoms to form a super-big circle unit. Each ring unit is connected to the adjacent six rings via an edge-sharing way to form a 2-D Cu/pz/pzc MOF layer, which is further extended along two spatial directions by two kinds of insert modes to generate an interpenetrating and staggered 3-D metal organic network. The {P₂W₁₈} clusters as nine-node inorganic guest molecules are grafted on the Cu/pz/pzc framework forming a complex 3D POMOF with a new topology {4·6·8³·10}₂ {4·6·8}₂ {4·6²·8²·10}₂{4·6³·8²}₂{4·8⁵}₂{4²·6²·8²}₂{4²·6³·8}{4³·6⁷·8¹³·10¹⁰·12³}₂ {4}₆{6·8²}₂{6²·8}₂ {6⁴·8·10}{6}₂{8}₄. Additionally, compound 1 exhibits good electrocatalytic activity for the reduction of H₂O₂ and effective photocatalytic degradation ability for three azo dyes under UV irradiation.