A two-dimensional cadmium(II) coordination polymer constructed from 4-carboxy-1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-5-carboxylate and 1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-4-carboxylate ligands.

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Crystals of poly[[aqua[μ3-4-carboxy-1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-5-carboxylato-κ5O1O1':N3,O4:O5][μ4-1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-4-carboxylato-κ7N3,O4:O4,O4':O1,O1':O1]cadmium(II)] monohydrate], {[Cd2(C15H14N2O4)(C16H14N2O6)(H2O)]·H2O}n or {[Cd2(Hcpimda)(cpima)(H2O)]·H2O}n, (I), were obtained from 1-(4-carboxybenzyl)-2-propyl-1H-imidazole-4,5-dicarboxylic acid (H3cpimda) and cadmium(II) chloride under hydrothermal conditions. The structure indicates that in-situ decarboxylation of H3cpimda occurred during the synthesis process. The asymmetric unit consists of two Cd2+ centres, one 4-carboxy-1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-5-carboxylate (Hcpimda2-) anion, one 1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-4-carboxylate (cpima2-) anion, one coordinated water molecule and one lattice water molecule. One Cd2+ centre, i.e. Cd1, is hexacoordinated and displays a slightly distorted octahedral CdN2O4 geometry. The other Cd centre, i.e. Cd2, is coordinated by seven O atoms originating from one Hcpimda2- ligand and three cpima2- ligands. This Cd2+ centre can be described as having a distorted capped octahedral coordination geometry. Two carboxylate groups of the benzoate moieties of two cpima2- ligands bridge between Cd2 centres to generate [Cd2O2] units, which are further linked by two cpima2- ligands to produce one-dimensional (1D) infinite chains based around large 26-membered rings. Meanwhile, adjacent Cd1 centres are linked by Hcpimda2- ligands to generate 1D zigzag chains. The two types of chains are linked through a μ2-η2 bidentate bridging mode from an O atom of an imidazole carboxylate unit of cpima2- to give a two-dimensional (2D) coordination polymer. The simplified 2D net structure can be described as a 3,6-coordinated net which has a (43)2(46.66.83) topology. Furthermore, the FT-IR spectroscopic properties, photoluminescence properties, powder X-ray diffraction (PXRD) pattern and thermogravimetric behaviour of the polymer have been investigated.