catena-Poly[copper(I)-bis[μ-3-(1H-imidazol-2-yl)pyridine]-copper(I)-di-μ-iodido]

The title polymeric compound, [Cu2I2(C8H7N3)2]n [C8H7N3 = 3-(1H-imidazol-2-yl)pyridine (HIPy), where HIPy comes from the in situ decarboxylation of 2-(pyridin-3-yl)-1H-imidazole-4,5-dicarboxylic acid (H3PyIDC)], was obtained under solvothermal conditions. Each CuI cation is in a distorted tetrahedral coordination environment defined by two iodide anions and two nitrogen atoms from two individual HIPy ligands. Two CuI atoms are connected by two HIPy ligands to form a dimer and these dimers are further bridged through the iodide atoms, leading to a chain structure extending parallel to [100]. Moreover, intermolecular N—H⋯I hydrogen bonds and weak π–π stacking interactions [centroid⋯centroid distances of 3.809 (4) Å, an interplanar separation of 3.345 (3) Å and a ring slippage of 1.822 Å] between pyridyl rings link the chains into a two-dimensional supramolecular network in the ac plane.

The author acknowledges the Young Teacher Training plan of Guangdong Universities (grant No. LYM09053, 2010, 01-2011

Comment
In recent years, in situ metal/ligand reactions have been widely investigated for the discovery of new organic reactions, elucidation of reaction mechanisms, as well as generation of novel coordination polymers (Chen et al., 2007). Among them, hydrothermal decarboxylation of N-heterocyclic carboxylic acid ligands has been shown to occur in the presence of metal ions (Sun et al., 2006;Yigit et al., 2006;Zhong et al., 2010). For example, Sun et al. (2006)  The asymmmetric unit of the title compound contains one Cu + cation, one Ianion and one HIPy neutral ligand. As shown in Fig. 1, the Cu I cation exhibits a distorted tetrahedral coordination, made up of two iodide anions and two nitrogen atoms from two individual HIPy ligands. The Cu···I bond lengths are 2.7331 (12) and 2.7887 (14) Å.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )