Tetraaquabis(isonicotinamide-κN 1)cobalt(II) bis(4-formylbenzoate) dihydrate

The asymmetric unit of the crystal structure of the title complex, [Co(C6H6N2O)2(H2O)4](C8H5O3)2·2H2O, contains one-half of the complex cation with the CoII ion located on an inversion center, a 4-formylbenzoate (FB) counter-anion and an uncoordinated water molecule. The four O atoms in the equatorial plane around the CoII ion form a slightly distorted square-planar arrangement with an average Co—O bond length of 2.086 Å; the slightly distorted octahedral coordination is completed by the two N atoms of the isonicotinamide (INA) ligands at a slightly longer distance [2.1603 (14) Å] in the axial positions. The dihedral angle between the carboxylate group and the attached benzene ring is 5.93 (13)°, while the pyridine and benzene rings are oriented at a dihedral angle of 3.09 (6)°. In the crystal structure, O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds link the molecules into a three-dimensional network. π–π Contacts between the benzene and pyridine rings [centroid–centroid distance = 3.758 (1) Å] may further stabilize the crystal structure.


Related literature
For general background to transition metal complexes of nicotinamide and/or the nicotinic acid derivative N,Ndiethylnicotinamide, see: Bigoli et al. (1972); Krishnamachari (1974).
The title compound is a monomeric complex, with Co II ion on a centre of symmetry, consisting of two INA ligands, four coordinated water molecules, two FB anions and two uncoordinated water molecules. In the title compound, INA ligands are monodentate. The 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 2.1603 (14) Å from the Co atom in the axial positions (Table 1, Fig. 1). The average Co-O bond length is 2.0861 (13) Å. The O-H···O hydrogen bond (Table 2) links the coordinated water molecule to the FB anion. The dihedral angle between the planar carboxylate group (O1/O2/C1) and the benzene ring A (C2-C7) is 5.93 (13)°, while that between rings A and B (N1/C8-C12) is 3.09 (6)°.
In the crystal structure, O-H···O, N-H···O and C-H···O hydrogen bonds (Table 2) link the molecules into a threedimensional network, in which they may be effective in the stabilization of the structure. The π-π contact between the benzene and pyridine rings, Cg1-Cg2, [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 distance of 3.758 (1) Å.

S2. Experimental
The title compound was prepared by the reaction of CoSO 4 .7H 2 O (1.41 g, 5 mmol) in H 2 O (25 ml) and INA (1.22 g, 10 mmol) in H 2 O (40 ml) with sodium 4-formylbenzoate (1.72 g, 10 mmol) in H 2 O (50 ml). The mixture was filtered and set aside to crystallize at ambient temperature for several days, giving orange single crystals.

S3. Refinement
Atoms H51, H52, H61, H62, H71 and H72 (for H 2 O) and H14 (for CH) were located in difference Fourier map and  The structure of the title molecule with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. Primed atoms are generated by the symmetry operator:(′) -x, -y, -z. Dashed line indicates the hydrogenbonding. 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.