Diaquadichloridobis(pyridine-κN)cobalt(II)

The title molecule, [CoCl2(C5H5N)2(H2O)2], has -1 symmetry with the CoII ion situated on an inversion centre. The cation has a distorted octahedral coordination environment and is surrounded by two N and two Cl atoms in the equatorial plane, while the coordinating water O atoms occupy the axial positions. The crystal exhibits nonmerohedral twinning with two domain states, the volume fractions of which were refined to 0.883 (2) and 0.117 (3). The crystal packing is stabilized by O—H⋯Cl hydrogen-bond interactions, forming two-dimensional networks lying parallel to (001). The crystal packing also features π–π interactions between the pyridine rings, with centroid–centroid separations of 3.493 (3) and 3.545 (3) Å.

Cobalt is essential and integral component of vitamin B12, therefore it is found in many tissues. Cobalt complexes are useful in nutritional supplementation.
Electron transfer as well as ligand substitution reactions of cobalt(II) complexes are useful in understanding of biochemistry of cobalt(II) (Milaeva et al., 2013). In order to study the electron transfer phenomena, the structure determination of the title compound, C 10 H 14 Cl 2 Co 1 N 2 O 2 , has been carried out.
The title molecule is shown in Fig. 1. It possesses symmetry 1 because its central atom Co(II) is situated at the crystallographic inversion centre. The Co(II) ion has a distorted octahedral coordination environment. It is surrounded by two N atoms and two Cl atoms in the equatorial plane, while the water oxygens occupy the axial positions.

Experimental
Diaquadichloridobis(pyridine-N)Cobalt(II) complex was prepared by dissolving cobalt(II) chloride hexahydrate (CoCl 2 .6H 2 O, 1 g, 0.28 M) in boiling ethanol (C 2 H 5 OH, 15 ml). An excess of pyridine (C 5 H 5 N, 2.5 ml, 10 M) dissolved in ethanol (2.0 ml), was added slowly to this mixture in order to precipitate the title complex. The crude pink coloured precipitate was washed with cold ethanol and then air-dried. Then this precipitate was dissolved in 10-15 ml of hot ethanol, cooled down and allowed to crystallize. After cooling pink coloured crystals (0.84 g) developed within 12 hours.
X-ray quality crystals were obtained by repeated recrystallization from hot ethanol. The typical size of the obtained block-like crystals was 0.8 × 0.6 × 0.5 mm. (The measured sample has been cut from a larger crystal.)

Refinement
After the solution of the phase problem by SHELXS-97 (Sheldrick, 2008), the refinement on HKLF4 (SHELXL-97, Sheldrick, 2008) converged to the R-factor equal to 0.067 for Fo>4σ(Fo). The difference electron density map showed several peaks of the order of magintude of 1eÅ -3 . A check by TwinRotMat (Bolte, 2004;PLATON (Spek, 2009)) showed that the crystal had a two-fold non-merohedral twinning with the twin matrix [h 2 k 2 l 2 ] = [h 1 k 1 l 1 ][-1 0 0.731 /0 -1 0.964/0 0 1]. The twin law generated from |F o | -|F c | table was used to generate HKLF5 format file (Bolte, 2004) which is suitable for a twin refinement by SHELXL-97 (Sheldrick, 2008). The refinement converged to the R-factor of 0.0474 for Fo>4σ(Fo). All the spurious difference peaks have vanished. The refined domain fractions converged to the values 0.883 (2) and 0.117 (3). As the second component of the twin was weak it was not observed during the cell indexing.
All the hydrogens were discernible in the difference electron density map. Nevertheless all the aryl hydrogens were fully constrained. The values of the used constraints were following: C aryl H = 0.93 Å. U iso H=1.2U eq C aryl . The positional parameters of the water hydrogens were restrained with O-H = 0.82 (1)Å, while U iso (H water-oxygen) =1.5U eq (O water_oxygen ).

Figure 1
View of the title molecule with the atom labelling scheme. The displacement ellipsoids are drawn at the 30% probability level while the H atoms are shown as small spheres of arbitrary radii. The atoms labelled by "a" are related by the symmetry operation -x, -y, -z.

Diaquadichloridobis(pyridine-κN)cobalt(II)
Crystal data [CoCl 2 (C 5  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.