Construction of Four Zn(II) Coordination Polymers Used as Catalysts for the Photodegradation of Organic Dyes in Water

Hydrothermal reactions of Zn(OAc)₂·2H₂O with flexible bipyridyl benzene ligand and three dicarboxylic derivatives gave rise to four new coordination polymers, [Zn₇(μ₄-O)₂(OAc)₁₀(bpmb)]_n (1), [Zn(5-OH-1,3-BDC)(bpmb)]_n (2), [Zn(1,2-BDC)(bpmb)]_n (3) and [Zn₂(ADB)₂(bpmb)]_n (4) (bpmb = 1,4-bis(pyridine-3-ylmethoxy)benzene, 5-OH-1,3-H₂BDC = 5-hydroxy-1,3-benzenedicarboxylic acid, 1,2-H₂BDC = 1,2-benzenedicarboxylic acid, H₂ADB = 2,2'-azodibenzoic acid). Their structures were characterized by single-crystal X-ray diffraction, elemental analyses, IR spectra, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). Compound 1 features a one-dimensional (1D) chain structure based on the rare heptanuclear [Zn₇(μ₄-O)(μ₃-OAc)₂(μ₂-OAc)₈] units. Compound 2 exhibits a novel 2D bilayer structure built from the two parallel 2D (4,4) layers. Compound 3 holds a 2D structure in which the 1,2-BDC ligands work as lockers interlocking 1D [Zn(bpmb)]_n chain. Compound 4 comprises a 3D framework constructed by 2D wrinkled [Zn₂(ADB)₄]_n networks and bpmb linkers with a six-connected pcu net. These results suggest that the motifs of the dicarboxylic ligands have significant effect on the final structures. These compounds exhibited relatively good photocatalytic activity towards the degradation of methylene blue (MB) in aqueous solution under a Xe lamp irradiation.