Diaquabis(4-methoxybenzoato-κO 1)bis(nicotinamide-κN 1)cobalt(II) dihydrate

In the mononuclear title compound, [Co(C8H7O3)2(C6H6N2O)2(H2O)2]·2H2O, the CoII ion is located on a crystallographic inversion center. The asymmetric unit is completed by one 4-methoxybenzoate anion, one nicotinamide (NA) ligand and one coordinated and one uncoordinated water molecule. All ligands act in a monodentate mode. The four O atoms in the equatorial plane around the CoII ion form a slightly distorted square-planar arrangement, while the slightly distorted octahedral coordination is completed by the two pyridine N atoms of the NA ligands in the axial positions. The dihedral angle between the carboxylate group and the attached benzene ring is 6.47 (7)°, while the pyridine and benzene rings are oriented at a dihedral angle of 72.80 (4)°. An O—H⋯O hydrogen bond links the uncoordinated water molecule to one of the carboxylate groups. In the crystal structure, intermolecular O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds link the molecules into a three-dimensional network.


Comment
As a part of our ongoing investigation on transition metal complexes of nicotinamide (NA), one form of niacin (Krishnamachari, 1974), and/or the nicotinic acid derivative N,N-diethylnicotinamide (DENA), an important respiratory stimulant (Bigoli et al., 1972), the title compound was synthesized and its crystal structure is reported herein.
The title compound, (I), is a mononuclear complex, where the Co II ion is located on a crystallographic inversion center. The asymmetric unit contains one 4-methoxybenzoate (PMOB) anion, one nicotinamide (NA) ligand and one coordinated and one uncoordinated water molecules, all ligands are monodentate ( Fig.   1 The four O atoms (O1, O5, and the symmetry-related atoms, O1', O5') in the equatorial plane around the Co II ion form a slightly distorted square-planar arrangement, while the slightly distorted octahedral coordination is completed by the two N atoms of the NA ligands (N1, N1') in the axial positions (Fig. 1). The near equality of the C1-O1 [1.2698 (14) Å] and C1-O2 [1.2626 (15) Å] bonds in the carboxylate group indicates a delocalized bonding arrangement, rather than localized single and double bonds. The average Co-O bond length is 2.0895 (9) Å, and the Co II ion is displaced out of the least-squares plane of the carboxylate group (O1/C1/O2) by 0.8407 (1) Å. The dihedral angle between the planar carboxylate group and the benzene ring A (C2-C7) is 6.47 (7)°, while that between rings A and B (N1/C9-C13) is 72.80 (4)°. An intramolecular O-H···O hydrogen bond (Table 1) links the uncoordinated water molecule to one of the carboxylate groups ( Fig. 1).
In the crystal structure, intermolecular O-H···O, N-H···O and C-H···O hydrogen bonds (Table 1) link the molecules into a three-dimensional network.

Experimental
The title compound was prepared by the reaction of CoSO 4 .7H 2 O (2.81 g, 10 mmol) in H 2 O (50 ml) and nicotinamide (2.44 g, 20 mmol) in H 2 O (50 ml) with sodium 4-methoxybenzoate (3.48 g, 20 mmol) in H 2 O (100 ml). The mixture was filtered and set aside to crystallize at ambient temperature for one week, giving pink single crystals.
supplementary materials sup-2 Refinement Atoms H21, H22 (for NH 2 ) and H51, H52, H61, H62 (for H 2 O) were located in a difference Fourier map and refined isotropically. The remaining H atoms were positioned geometrically with C-H = 0.95 and 0.98 Å for aromatic and methyl H atoms and constrained to ride on their parent atoms, with U iso (H) = xU eq (C), where x = 1.5 for methyl H and x = 1.2 for aromatic H atoms. Fig. 1. The molecular structure of the title compound 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 lines indicate the hydrogen-bonding.

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.