Diaquabis(2-chlorobenzoato-κO)bis(nicotinamide-κN 1)nickel(II)

The title NiII complex, [Ni(C7H4ClO2)2(C6H6N2O)2(H2O)2], is centrosymmetric with the Ni atom located on an inversion centre. The molecule contains two 2-chlorobenzoate (CB) and two nicotinamide (NA) ligands and two water molecules, all ligands being monodentate. The four O atoms in the equatorial plane around the Ni atom form a slightly distorted square-planar arrangement, while the slightly distorted octahedral coordination is completed by the two N atoms of the NA ligands in the axial positions. The dihedral angle between the carboxyl group and the adjacent benzene ring is 29.48 (16)°, while the pyridine and benzene rings are oriented at a dihedral angle of 83.16 (5)°. In the crystal structure, O—H⋯O and N—H⋯O hydrogen bonds link the molecules into infinite chains. π–π Contacts between the benzene and pyridine rings [centroid–centroid distance = 3.952 (1) Å] may further stabilize the crystal structure. There is also a C—H⋯π interaction.


Comment
Transition metal complexes with biochemically active ligands frequently show interesting physical and/or chemical properties, as a result they may find applications in biological systems (Antolini et al., 1982). The structural functions and coordination relationships of the arylcarboxylate ion in transition metal complexes of benzoic acid derivatives change depending on the nature and position of the substituent groups on the benzene ring, the nature of the additional ligand molecule or solvent, and the medium of the synthesis Shnulin et al., 1981). Nicotinamide (NA) is one form of niacin and a deficiency of this vitamin leads to loss of copper from the body, known as pellagra disease. Victims of pellagra show unusually high serum and urinary copper levels (Krishnamachari, 1974). On the other hand, the nicotinic acid derivative N,N-diethylnicotinamide (DENA) is an important respiratory stimulant (Bigoli et al., 1972).
The structure determination of the title compound, (I), a nickel complex with two 2-chlorobenzoate (CB), two nicotinamide (NA) ligands and two water molecules, was undertaken in order to determine the properties of the ligands and also to compare the results obtained with those reported previously.
Compound (I) is a monomeric complex, with the Ni atom on a centre of symmetry. It contains two CB, two NA ligands and two water molecules (Fig. 1). All ligands are monodentate. The four O atoms (O1, O4, and the symmetry-related atoms, O1', O4') in the equatorial plane around the Ni atom 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 (Table   1 and Fig. 1). The intramolecular O-H···O hydrogen bonds ( Table 2)  In the crystal structure, intermolecular O-H···O and N-H···O hydrogen bonds (Table 2) link the molecules into infinite chains (Fig. 2), in which they may be effective in the stabilization of the structure. The π-π contacts between the 2-chlorobenzoate rings and the pyridine rings of NA ligands, Cg2-Cg1 i [symmetry code: (i) x -1/2, 1/2 -y, 1/2 + z, where Cg1 and Cg2 are centroids of the rings A (C2-C7) and B (N1/C9-C13), respectively] may further stabilize the structure, with centroid-centroid distance of 3.952 (1) Å. There is also a C-H···π interaction (Table 2).

Experimental
The title compound was prepared by the reaction of Ni(SO 4 ).6(H 2 O) (1.31 g, 5 mmol) in H 2 O (20 ml) and NA (1.22 g, 10 mmol) in H 2 O (20 ml) with sodium 2-chlorobenzoate (1.785 g, 10 mmol) in H 2 O (50 ml). The mixture was filtered and set aside to crystallize at ambient temperature for 5 d, giving orange single crystals.

Refinement
H atoms of water molecule and NH 2 group were located in difference Fourier maps and refined isotropically, with restrain of O4-H42 = 0.850 (18) Å. The remaining H atoms were positioned geometrically with C-H = 0.93 Å, for aromatic H atoms and constrained to ride on their parent atoms, with U iso (H) = 1.2U eq (C). Fig. 1. The molecular structure of the title molecule with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen bonds are shown as dashed lines. Primed atoms are generated by the symmetry operator (1 -x, -y, -z).   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 Rfactors(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