trans-Tetraaquabis(isonicotinamide-κN 1)cobalt(II) bis(3-hydroxybenzoate) tetrahydrate

The asymmetric unit of the title compound, [Co(C6H6N2O)2(H2O)4](C7H5O3)2·4H2O, contains one-half of the complex cation with the CoII ion located on an inversion center, a 3-hydroxybenzoate counter-anion and two uncoordinated water molecules. Four water O atoms in the equatorial plane around the CoII ion [Co—O = 2.0593 (16) and 2.1118 (16) Å] form a slightly distorted square-planar arrangement, and the distorted octahedral geometry is completed by the two N atoms [Co—N = 2.1306 (18) Å] from two isonicotinamide ligands. In the anion, the carboxylate group is twisted from the attached benzene ring at 8.84 (17)°. In the crystal, a three-dimensional hydrogen-bonding network, formed by classical O—H⋯O and N—H⋯O hydrogen bonds, consolidates the crystal packing, which exhibits π–π interactions between the benzene and pyridine rings, with centroid–centroid distances of 3.458 (1) and 3.606 (1) Å, respectively.

The title compound (I) is isostructural with the related Ni complex (Zaman et al., 2012). In (I) (Fig. 1), four O atoms (O5, O6, and the symmetry-related atoms, O5′, O6′) in the equatorial plane around the Co atom form a slightly distorted square-planar arrangement, while the slightly distorted octahedral coordination is completed by the two pyridine N atoms (N1, N1′) of the INA ligands at 2.1306 (18) Å from the Co atom in the axial positions (Fig. 1) to the HB anion. The dihedral angle between the planar carboxylate group (O1/O2/C1) and the benzene ring A (C2-C7) is 8.84 (17)°, while that between rings A and B (N1/C8-C12) is 1.24 (7)°.
In the crystal structure, intermolecular O-H···O and N-H···O hydrogen bonds (Table 1) link the molecules into a three-dimensional network, in which they may be effective in the stabilization of the structure. π-π Contacts between the benzene and pyridine rings, Cg1-Cg2 and Cg1-Cg2 i , [symmetry code: (i) -1 + x, y, z, where Cg1 and Cg2 are centroids of the rings A (C2-C7) and B (N1/C8-C12), respectively] may further stabilize the structure, with centroid-centroid distances of 3.606 (1) and 3.458 (1) Å, respectively.

Experimental
The title compound was prepared by the reaction of CoSO 4 .7H 2 O (1.406 g, 5 mmol) in H 2 O (100 ml) and INA (1.220 g, 10 mmol) in H 2 O (50 ml) with sodium 3-hydroxybenzoate (1.601 g, 10 mmol) in H 2 O (100 ml). The mixture was filtered and set aside to crystallize at ambient temperature for three weeks, giving orange single crystals.

Figure 1
The molecular structure of (I) with the atom-numbering scheme [symmetry code: (′) -x, -y, -z]. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen bonds are shown as dashed lines.

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.