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.

Crystals of poly[[aqua[μ3 -4-carboxy-1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-5-carboxylato-κ5 O1 O1' :N3 ,O4 :O5 ][μ4 -1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-4-carboxylato-κ7 N3 ,O4 :O4 ,O4' :O1 ,O1' :O1 ]cadmium(II)] monohydrate], {[Cd2 (C15 H14 N2 O4 )(C16 H14 N2 O6 )(H2 O)]·H2 O}n or {[Cd2 (Hcpimda)(cpima)(H2 O)]·H2 O}n , (I), were obtained from 1-(4-carboxybenzyl)-2-propyl-1H-imidazole-4,5-dicarboxylic acid (H3 cpimda) and cadmium(II) chloride under hydrothermal conditions. The structure indicates that in-situ decarboxylation of H3 cpimda 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 CdN2 O4 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 [Cd2 O2 ] 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.