trans-Diaquabis(pyridazine-3-carboxylato-κ2 N 2,O)cobalt(II) dihydrate

The title compound, [Co(C5H3N2O2)2(H2O)2]·2H2O, contains a CoII ion on an inversion center, exhibiting an octahedral coordination geometry. The equatorial plane is formed by two trans-related N,O-bidentate pyridazine-3-carboxylate ligands and the axial positions are occupied by two water molecules. The CoII complex molecules are stacked in a column along the a-axis direction by an O—H⋯N hydrogen bond between the non-coordinating pyridazine N atom and the coordinating water molecule. These columns are further connected into a layer parallel to the ac plane by additional hydrogen bonds involving the coordinating and non-coordinating water molecules, and the non-coordinating carboxylate O atom. The crystal packing is completed by interlayer weak C—H⋯O interactions.

The title compound, [Co(C 5 H 3 N 2 O 2 ) 2 (H 2 O) 2 ]Á2H 2 O, contains a Co II ion on an inversion center, exhibiting an octahedral coordination geometry. The equatorial plane is formed by two trans-related N,O-bidentate pyridazine-3-carboxylate ligands and the axial positions are occupied by two water molecules. The Co II complex molecules are stacked in a column along the a-axis direction by an O-HÁ Á ÁN hydrogen bond between the non-coordinating pyridazine N atom and the coordinating water molecule. These columns are further connected into a layer parallel to the ac plane by additional hydrogen bonds involving the coordinating and non-coordinating water molecules, and the non-coordinating carboxylate O atom. The crystal packing is completed by interlayer weak C-HÁ Á ÁO interactions.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: IS5284). metal-organic compounds m420 Artetxe et al.

Gutiérrez-Zorrilla Comment
The title compound, trans-[Co (C 4 .2H 2 O, crystallizes in the triclinic crystal system, space group P-1, and it is isostructural with the zinc and manganese complexes previously reported by Gryz et al. (2003) and Ardiwlnata et al. (1989). As expected, the Co-O and Co-N distances (Table 1) are similar to those of the Zn(II) and Mn(II) analogues.

Experimental
To a solution of CoCl 2 .6H 2 O (71 mg, 0.3 mmol) in water (15 ml) 3-pyridazine carboxylic acid (74 mg, 0.6 mmol) was added and the resulting solution was stirred for 30 min at 90 °C. Prismatic orange crystals were obtained by slow evaporation after two days.

Refinement
H atoms of the water molecules were located in a Fourier difference map and refined isotropically with O-H bond lengths restrained to 0.84 (2) Å. All H atoms of the pyridazine ring were positioned geometrically and refined using a riding model with C-H = 0.95 Å and U iso (H) = 1.2U eq (C).

Computing details
Data collection: CrysAlis PRO (Agilent, 2011); cell refinement: CrysAlis PRO (Agilent, 2011); data reduction: CrysAlis PRO (Agilent, 2011); program(s) used to solve structure: OLEX2 (Dolomanov et al., 2009); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012) and PLATON (Spek, 2009 -3-carboxylato-κ 2 N 2 ,O)  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.