Poly[[(μ2-benzene-1,3-dicarboxylato){μ2-1,4-bis[(1H-imidazol-1-yl)methyl]benzene}cadmium] dimethylformamide monosolvate]

The title coordination polymer, {[Cd(C8H4O4)(C14H14N4)]·C3H7NO}n, was synthesized by solvothermal reaction of metallic cadmium with the semi-rigid neutral ligand 1,4-bis[(1H-imidazol-1-yl)methyl]benzene (bix) and the V-shaped benzene-1,3-dicarboxylic acid (m-H2bdc). The structure exhibits a pseudo-C-centring which is almost fulfilled by the polymeric metal complex but not by the solvent dimethylformamide (DMF) molecules. The asymmetric unit contains two independent CdII ions, two m-bdc2− ligands, one and two half bix ligands, and two solvent DMF molecules. The CdII ions are both five-coordinated by three O atoms from two different m-bdc2− ligands and two N atoms from two different bix ligands in a distorted square-pyramidal geometry. The m-bdc2− ligands adopt a chelate-monodentate coordination mode, connecting neighboring CdII ions into a zigzag chain parallel to [110]. Adjacent chains are further cross-linked by bix ligands, giving rise to a puckered sheet nearly perpendicular to the chain direction. Thus, each CdII ion is connected to four neighboring CdII ions through two m-bdc2− anions and two bix ligands, giving rise to the final non-interpenetrating uninodal layer with sql (4,4) topology.

The title coordination polymer, {[Cd(C 8 H 4 O 4 )(C 14 H 14 N 4 )]Á-C 3 H 7 NO} n , was synthesized by solvothermal reaction of metallic cadmium with the semi-rigid neutral ligand 1,4bis[(1H-imidazol-1-yl)methyl]benzene (bix) and the V-shaped benzene-1,3-dicarboxylic acid (m-H 2 bdc). The structure exhibits a pseudo-C-centring which is almost fulfilled by the polymeric metal complex but not by the solvent dimethylformamide (DMF) molecules. The asymmetric unit contains two independent Cd II ions, two m-bdc 2À ligands, one and two half bix ligands, and two solvent DMF molecules. The Cd II ions are both five-coordinated by three O atoms from two different mbdc 2À ligands and two N atoms from two different bix ligands in a distorted square-pyramidal geometry. The m-bdc 2À ligands adopt a chelate-monodentate coordination mode, connecting neighboring Cd II ions into a zigzag chain parallel to [110]. Adjacent chains are further cross-linked by bix ligands, giving rise to a puckered sheet nearly perpendicular to the chain direction. Thus, each Cd II ion is connected to four neighboring Cd II ions through two m-bdc 2À anions and two bix ligands, giving rise to the final non-interpenetrating uninodal layer with sql (4,4) topology.

Experimental
Crystal data [Cd(C 8

Comment
Studies of metal-organic coordination polymers (MOCPs) are of considerable interest due to their intrinsically interesting structures and fascinating network topologies (Batten et al., 1998), and potential applications in storage (Chen et al., 2011), catalysis (Farrusseng et al., 2009), molecular magnetism (Kurmoo, 2009), recognition (Pramanik et al., 2011), and photoluminescence (Wong et al., 2006. An important motivation for this field is the rational design and preparation of crystalline solid material with peculiar topology and desired functions. The design possibilities of organic ligands and the coordination tendencies of metal ions have led to a large number of novel structural features quite often endowed with unique properties. Aromatic multi-acids are good connectors in constructed excellent porous coordination polymers due to their rigidity in conformation and various coordination modes. In particular, the combination of multicarboxylate anions with N-donor auxiliary ligands is a good choice for the construction of novel topology and networks. In the present case, we used the benzene-1,3-dicarboxylic acid (m-H 2 bdc) as anionic ligand and 1,4-bis(imidazol-l-ylmethyl)benzene (bix) as ancillary ligand to construct a novel two-dimensional coordination polymer.
The structure shows pseudo-symmetry, in which the atoms in the main framework fulfill the pseudo-C centring and the DMF molecules break this pseudo-symmetry. The asymmetric unit contains two crystallographically independent Cd(II) ions, two m-bdc 2ligands, one and two halves bix ligands, and two lattice DMF molecules (Fig. 1). Cd1 and Cd2 have the same coordination environment. They are five-coordinated by three oxygen atoms from two different m-bdc 2ligands and two nitrogen atoms from two different bix ligands. The distortion parameters τ 5 of 0.335 for both Cd1 and Cd2 indicate that the coordination environment corresponds to a distorted square pyramid; expected values are τ = 0 for a square pyramid and τ = 1 for an ideal trigonal bipyramid (Addison et al., 1984).
As shown in Fig. 2 EtOH, and dried under ambient conditions with a yield of 13% based on Cd).

Refinement
All the hydrogen atoms attached to carbon atoms were placed in calculated positions and refined as the riding model.  Sheldrick, 2008) and DIAMOND (Brandenburg, 1999); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figure 1
The asymmetric unit of the compound. Displacement ellipsoids are drawn at the 30% probability level. Symmetry codes:

Figure 2
View of the single layer with the (4,4)-topology.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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 R-factors(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.