Bis(3-aminopyrazine-2-carboxylato-κ2 N 1,O)diaquacobalt(II)

In the title compound, [Co(C5H4N3O2)2(H2O)2], the CoII atom is situated on a twofold rotation axis and is N,O-chelated by two 3-aminopyrazine-2-carboxylate anions and additionally bonded to the O atoms of two water molecules, leading to a slightly distorted octahedral coordination environment. The crystal packing is dominated by intermolecular O—H⋯O, O—H⋯N and N—H⋯O hydrogen bonding involving the water molecules and amino groups as donors and carboxylate O atoms, as well as the non-coordinating heterocyclic N atoms as acceptors, resulting in a three-dimensional network. An intramolecular N—H⋯O hydrogen bond is also observed.

In the title compound, [Co(C 5 H 4 N 3 O 2 ) 2 (H 2 O) 2 ], the Co II atom is situated on a twofold rotation axis and is N,O-chelated by two 3-aminopyrazine-2-carboxylate anions and additionally bonded to the O atoms of two water molecules, leading to a slightly distorted octahedral coordination environment. The crystal packing is dominated by intermolecular O-HÁ Á ÁO, O-HÁ Á ÁN and N-HÁ Á ÁO hydrogen bonding involving the water molecules and amino groups as donors and carboxylate O atoms, as well as the non-coordinating heterocyclic N atoms as acceptors, resulting in a three-dimensional network. An intramolecular N-HÁ Á ÁO hydrogen bond is also observed.
In continuation of our investigations on the influence of hydrogen bonds on the structural features (Bouacida et al., 2007(Bouacida et al., ,2009, we report here the crystal growth and crystal structure of the title compound, [Co(C 5 The asymmetric unit of (I) consists of one-half of the complex molecule, with the other half being generated by a twofold rotation axis running through the Co II atom (Wyckoff site 4 e). The latter is octahedrally coordinated by two 3aminopyrazine-2-carboxylate anions acting in a bidentate manner and by two water molecules. The molecular geometry and the atom-numbering scheme of (I) are shown in Fig. 1.
Bond lengths and angles observed in the different entities show normal features and are consistent with those reported previously for related systems (Shi et al., 2011). Fig. 2 shows a packing diagram of the structure. Parallel to the c axis channels with a square cross-section are formed. The crystal packing can be described by stacking of alternating layers parallel to (110). The layers are linked together by O1W-H···N, O1W-H···O and N-H···O interactions involving the water molecules and amino functions as donors and carboxylate O atoms as well as the non-coordinating heterocyclic N atoms as acceptors (Fig. 3, Table 1). These interactions lead to the formation of a three-dimensional network.

Experimental
The title compound was obtained from a mixture of cobalt(II) chloride hexahydrate (0.05 g, 0.2 mmol), 3-aminopyrazine-2-carboxylic acid (0.03 g, 0.2 mmol) and acidified water (25 ml, HCl 37%). The solution was evaporated at room temperature for two weeks. Yellow single crystals were obtained and were carefully isolated under a polarizing microscope for analysis by X-ray diffraction.

Refinement
The H atoms were localized in Fourier maps but were eventually introduced in calculated positions and treated as riding on their parent atoms (C or N) with C-H = 0.93 Å and N-H = 0.86 Å with U iso (H) = 1.2U eq (C or N). The water H atoms H1W and H2W were also located in a difference Fourier map. Their positions were refined freely, but their temperature factors were refined isotropically with U iso (H) = 1.5U eq (OW).

Figure 1
A view of the coordination environment of the Co II atom of (I) with the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms are represented as small spheres of arbitrary radius. [Symmetry code: (i)- x, y, -z + 3/2.]

Figure 2
The packing of the structure of (I) viewed along the c axis  Hydrogen bonding interactions (dashed lines) in the structure of (I)

Bis(3-aminopyrazine-2-carboxylato-κ 2 N 1 ,O)diaquacobalt(II)
Crystal data [Co(C 5  Hydrogen site location: inferred from neighbouring sites H atoms treated by a mixture of independent and constrained refinement w = 1/[σ 2 (F o 2 ) + (0.0413P) 2 ] where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.48 e Å −3 Δρ min = −0.38 e Å −3 Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq