Diaquabis(2-bromobenzoato-κO)bis(N,N-diethylnicotinamide-κN 1)nickel(II)

In the monomeric centrosymmetric title NiII complex, [Ni(C7H4BrO2)2(C10H14N2O)2(H2O)2], the NiII ion is located on an inversion center. The asymmetric unit contains one 2-bromobenzoate ligand, one diethylnicotinamide (DENA) ligand and one coordinated water molecule. The four O atoms in the equatorial plane around the NiII ion form a slightly distorted square-planar arrangement, while the slightly distorted octahedral coordination is completed by two N atoms of two DENA ligands in the axial positions. The dihedral angle between the benzene ring and the attached carboxylate group is 87.73 (15)°, while the pyridine and benzene rings are oriented at a dihedral angle of 42.48 (7)°. In the crystal structure, O—H⋯O hydrogen bonds link the molecules into a two-dimensional network parallel to (10). In addition, C—H⋯O hydrogen bonds are observed.

In the monomeric centrosymmetric title Ni II complex, [Ni(C 7 H 4 BrO 2 ) 2 (C 10 H 14 N 2 O) 2 (H 2 O) 2 ], the Ni II ion is located on an inversion center. The asymmetric unit contains one 2bromobenzoate ligand, one diethylnicotinamide (DENA) ligand and one coordinated water molecule. The four O atoms in the equatorial plane around the Ni II ion form a slightly distorted square-planar arrangement, while the slightly distorted octahedral coordination is completed by two N atoms of two DENA ligands in the axial positions. The dihedral angle between the benzene ring and the attached carboxylate group is 87.73 (15) , while the pyridine and benzene rings are oriented at a dihedral angle of 42.48 (7) . In the crystal structure, O-HÁ Á ÁO hydrogen bonds link the molecules into a two-dimensional network parallel to (101). In addition, C-HÁ Á ÁO hydrogen bonds are observed.

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). 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-bromobenzoate (BB), two diethylnicotinamide (DENA) 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 II ion on a centre of symmetry ( 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 two N atoms of two DENA ligands (N1, N1') in axial positions (Table 1 and  In the crystal structure, intermolecular O-H···O hydrogen bonds (Table 2) link the molecules into a two-dimensional network parallel to the (1 0 1). In addition, C-H···O hydrogen bonds are observed.

Experimental
The title compound was prepared by the reaction of NiSO 4 .6H 2 O (1.31 g, 5 mmol) in H 2 O (20 ml) and i>N,N-diethylnicotinamide (1.78 g, 10 mmol) in H 2 O (20 ml) with sodium 2-bromobenzoate (2.23 g, 10 mmol) in H 2 O (50 ml). The mixture was filtered and set aside to crystallize at ambient temperature for 2 d, giving blue single crystals.

Refinement
H atoms of water molecule were located in difference Fourier maps and refined isotropically. The remaining H atoms were positioned geometrically with C-H = 0.93, 0.97 and 0.96 Å for aromatic, methylene 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 all other 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 (1 -x, -y, -z).