catena-Poly[[bis(1H-imidazole-κN3)copper(II)]-μ-benzene-1,4-dicarboxylato-κ2 O 1:O 4]

In the title compound, [Cu(C8H4O4)(C3H4N2)2]n, the CuII atom is four-coordinated by two carboxylate O atoms from two different terephthalate ligands and two N atoms from two imidazole ligands in a slightly distorted square-planar coordination environment. Each terephthalate ligand acts as a bis-monodentate ligand that binds two CuII atoms, thus forming two unique chains extending parallel to [110]. The imidazole ligands are attached on both sides of the chains.

In the title compound, [Cu(C 8 H 4 O 4 )(C 3 H 4 N 2 ) 2 ] n , the Cu II atom is four-coordinated by two carboxylate O atoms from two different terephthalate ligands and two N atoms from two imidazole ligands in a slightly distorted square-planar coordination environment. Each terephthalate ligand acts as a bis-monodentate ligand that binds two Cu II atoms, thus forming two unique chains extending parallel to [110]. The imidazole ligands are attached on both sides of the chains.

Comment
Dielectric constant measurements of compounds as a function of temperature is the basic method to find potential ferroelectric phase change materials (Fu et al., 2009;Ye et al., 2006;Zhang et al., 2008;Zhang et al., 2010). Unfortunately, the study carried out on the title compound indicated that the permittivity is temperature-independent, suggesting that there may be no dielectric disuniformity between 80 K to 350 K (m.p. 393-381 K). In this report the crystal structure of the title compound is reported.
An ORTEP diagram showing the structure of the title compound with the symmetry related fragments and atom-numbering scheme is shown in Fig. 1. The Cu(II) atom,with an inversion center, adopts a distorted octahedral geometry comprising two nitrogen atoms of two pyrazole ligands [Cu1-N1 = 1.9859 (19) Å] and two oxygen atoms of two different tp ligands [Cu1-O1 = 1.9408 (14) Å]. The N2O2 moiety defines the equatorial plane of the octahedron. In the equatorial plane, the angles between the cis-positioned atoms are close to 90° and those of the transpositioned atoms are identical to 180° since the Cu atom resides at the inversion center.

Experimental
An aqueous solution of imidazole (1.64 g, 20 mmol) and terephthalic acid (10 mmol) was treated with CuCl 2 (1.35 g, 10 mmol). After the mixture was churned for a few minutes, slow evaporation of the resulting solution yielded blue crystals after a few days.

Refinement
All H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms except H2A with C-H = 0.93 Å, with U iso (H) = 1.2 U iso (C). Fig. 1. The molecular structure of the title compound, showing the atomic numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. Symmetry codes for A: 1 -x, 2 -y, 2 -z. Symmetry codes for B: 1.5 -x, 1.5 -y, 2 -z. Symmetry codes for C: 0.5 -x, 2.5 -y, 2 -z.  Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.