Diaquadichlorido[5-(3-pyridinio)tetrazolato-κN 2]copper(II) dihydrate

The title compound, [CuCl2(C6H5N5)2(H2O)2]·2H2O, was synthesized by hydrothermal reaction of CuCl2 with 3-(2H-tetrazol-5-yl)pyridine. The CuII cation, located on an inversion center, is coordinated by two Cl− ions, two N atoms from two 5-(3-pyridinio)tetrazolate zwitterions and two O atoms from two water molecules in a distorted octahedral geometry. In the crystal, molecules are linked into a two-dimensional sheet parallel to (001) by N—H⋯N, O—H⋯N, O—H⋯O and O—H⋯Cl hydrogen bonds involving the pyridinium N atom, the Cl atoms and the coordinated and free water molecules. The latter are disordered over two positions in a 0.54:0.46 ratio.

The title compound, [CuCl 2 (C 6 H 5 N 5 ) 2 (H 2 O) 2 ]Á2H 2 O, was synthesized by hydrothermal reaction of CuCl 2 with 3-(2Htetrazol-5-yl)pyridine. The Cu II cation, located on an inversion center, is coordinated by two Cl À ions, two N atoms from two 5-(3-pyridinio)tetrazolate zwitterions and two O atoms from two water molecules in a distorted octahedral geometry. In the crystal, molecules are linked into a two-dimensional sheet parallel to (001) by N-HÁ Á ÁN, O-HÁ Á ÁN, O-HÁ Á ÁO and O-HÁ Á ÁCl hydrogen bonds involving the pyridinium N atom, the Cl atoms and the coordinated and free water molecules. The latter are disordered over two positions in a 0.54:0.46 ratio.

Comment
The construction of metal-organic coordination compounds has attracted much attention owing to the potential functions, such as permittivity, fluorescence, magnetism and optical properties. (Chen et al., 2000;Chen et al., 2001;Fu et al., 2007;Liu et al., 1999;Xie et al., 2003;Xie et al., 2002;Zhang et al., 2001;Zhao et al., 2004) Tetrazole compounds are a class of excellent ligands for the construction of novel metal-organic frameworks, because of its various coordination modes. (Wang, et al. 2005;. We report here the crystal structure of the title compound, Diaqua- The Cu II cation, located on an inversion center, is coordinated by two Clions, two N atoms from two pyridinio-4-(2Htetrazolate) zwitterions and two O atoms from two water molecules in a distorted octahedral geometry. The pyridine N atom of the organic ligand is protonated. The pyridinium and tetrazolate rings are essentially coplanar, with a dihedral angle of 0.76 (1)°. The geometric parameters of the tetrazolate ring are comparable to those in related molecules (Wang, et al. 2005;. The molecules are linked into a two-dimensional sheet parallel to the (0 0 1) plane by intermolecular N-H···N, O-H···N, O-H···O and O-H···Cl hydrogen bonds involving the pydine nitrogen and the coordinated and free water molecules. (Table   1 and Fig.2).

Refinement
All H atoms attached to C atoms and N atom were fixed geometrically and treated as riding with C-H = 0.93 Å and N-H = 0.86 Å with U iso (H) = 1.2U eq (C or N). H atoms of water molecule were located in difference Fourier maps and included in the subsequent refinement using restraints (O-H= 0.85 (1)Å and H···H= 1.39 (2)Å) with U iso (H) = 1.5U eq (O). In the last stage of refinement, these H atoms were treated as riding on their parent O atom.
The free water molecule was found to be roughly staistically disoredered over two positions. H atoms for this disordered molecules were treated as above.

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.