catena-Poly[cobalt(II)-di-μ-chlorido-κCl:Cl-μ-1,5-dimethyl-1H-tetra-zole-κN:N]: an X-ray powder investigation.

The asymmetric unit of the title compound, [CoCl(2)(C(3)H(6)N(4))](n), contains two Co atoms, both lying on inversion centres, two Cl atoms and one 1,5-dimethyl-tetra-zole ligand. The coordination polyhedra of both Co atoms adopt flattened octa-hedral geometry, with two N atoms from two ligands in axial positions and four Cl atoms in equatorial sites. Neighbouring Co atoms are linked together via two bridging Cl atoms and one tetra-zole ring to form polymeric chains running along the a axis.

The asymmetric unit of the title compound, [CoCl 2 (C 3 H 6 N 4 )] n , contains two Co atoms, both lying on inversion centres, two Cl atoms and one 1,5-dimethyltetrazole ligand. The coordination polyhedra of both Co atoms adopt flattened octahedral geometry, with two N atoms from two ligands in axial positions and four Cl atoms in equatorial sites. Neighbouring Co atoms are linked together via two bridging Cl atoms and one tetrazole ring to form polymeric chains running along the a axis.

Related literature
For the crystal structure of a related Cu complex, see: Ivashkevich et al. (2006). For values of radii for ions with octahedral coordination and molecular geometric parameters, see: Shannon (1976) and Allen (2002), respectively. For details of the indexing algorithm, see: Werner et al. (1985).

Comment
In our previous paper (Ivashkevich et al., 2006) we reported the crystal structure of copper(II) chloride complex with 1,5dimethyltetrazole, CuCl 2 L. That was the first experimental findings of bridge coordination of 1,5-disubstituted tetrazoles through the tetrazole ring bridge N3-N4. In the present work, we report another example of such type complexes, namely the title complex of cobalt(II) chloride with 1,5-dimethyltetrazole, (I).
Complex (I) has a 1:1 metal-to-ligand ratio of cobalt(II) with the 1,5-dimethyltetrazole. The asymmetric unit contains two Co atoms, both lying on inversion centres, two Cl atoms and one 1,5-dimethyltetrazole molecule, all in general positions.
Co1 is bonded to the tetrazole ring atoms N4, whereas Co2 coordinates the tetrazole ring atoms N3 (Fig. 1). The tetrazole ring geometry is typical of 1-and 1,5-substituted tetrazoles. The complex is a one-dimensional coordination polymer, with polymeric chains running along the a axis ( Fig.1,2). The chains are formed due to chloride bridges and the tetrazole ring bridges N3-N4 between the neighbouring Co atoms.
Complex (I) is isotypic with the above copper(II) analogue, and it is of interest to compare the structures of the compounds. Whereas Cu coordination octahedra show essential elongation of axial Cu-Cl bonds compared to equatorial Cu-Cl and Cu-N ones, Co octahedra are flattened, with axial Co-N bonds and very similar in lengths equatorial Co-Cl bonds. In Co1 and Co2 octahedra, the difference between the axial and equatorial bond lengths (Table 1), being much less than that in the Cu octahedra, may be related to difference in size of Cl and N atoms. However, essential elongation of the Cu octahedra is probably induced by the Jahn-Teller effect. In complex (I), closely spaced values of all Co-Cl bond lengths are responsible for rather symmetrical chloride bridges between the neighbouring Co atoms in polymeric chains, in contrast to copper(II) analogue with non-symmetrical chloride bridges.
Comparing the cell volumes of the two isotypic compounds [374.15 (4) Å 3 for Cu complex and 376.72 (4) Å 3 for Co one and taking into account octahedral ionic radii (Shannon, 1976) of Cu II (0.73 Å) and Co II (0.65 Å for low-spin state and 0.75 Å for high-spin state), one may expect that cations Co II in complex(I) are in high-spin state at room temperature. This conclusion is confirmed by EPR investigation of the complex, which does not reveal EPR spectra at room temperature. As known, Co II cations in high-spin state shows EPR signals only at very low temperatures.

Refinement
For complex (I), a triclinic unit cell (a = 6.728, b = 7.596, c = 8.764 Å, α = 109.62, β = 102.96, γ = 105.70°) was determined using the indexing program TREOR90 (Werner et al., 1985). The obtained values as well as observed resemblance of powder patterns indicated isotypism of (I) with investigated earlier coordination polymers CuCl 2 L, where L = 1,5-dimethyltetrazole, crystallizing in the space group P1 (Ivashkevich et al., 2006). This space group and the atomic coordinates of the above copper(II) complex were used as starting parameters for the Rietveld refinement of (I) with the FULLPROF program (Rodríguez-Carvajal, 2001). However, the refinement found difficulty in reaching the agreement of experimental and calculated intensities of reflections. From this fact an assumption was made that the above unit-cell dimensions were inconsistent with the initial atomic coordinates. Search for alternative unit cells resulted in the following cell: a' = 6.728, b' = 7.596, c' = 8.997 Å; α' = 108.35, β' = 107.50, γ' = 105.70°, which is of the same volume and related to the first one by the vector transformation a' =-a, b' =-b, c' = a + b + c. This cell provided a good agreement of the observed and calculated intensities.
Background intensity was found by Fourier filtering technique as implemented in the FULLPROF program, under visual inspection of the resulting background curve. Correction for profile asymmetry was made for reflections up to 2θ=25°.
The H atoms of the methyl groups were placed in geometrically calculated positions using the program SHELXL97 (Sheldrick, 2008), with displacement parameter B iso (H)=1.5B iso (C). Non-H atoms were refined isotropically. Four independent B iso parameters were employed: one for the two Co, one for the two Cl atoms, one for all N and C atoms of the tetrazole ring, and one for the C atoms of the methyl groups.
For the refinement, suitable restraints were imposed on bond lengths of the ligand molecule, based on a geometry analysis of 1,5-alkyltetrazoles (Cambridge Structural Database, version 5.29 of November 2007;Allen, 2002). The restraints were set as d(3σ), where d are mean values of bond distances resulting from a CSD survey, and σ are their s.u. values. For the refined atomic coordinates of (I), the s.u. values are taken from the software and likely to be underestimated.