Diaquabis(N,N-diethylnicotinamide-κN 1)bis(4-formylbenzoato-κO)nickel(II)

In the title centrosymmetric mononuclear NiII compound, [Ni(C8H5O3)2(C10H14N2O)2(H2O)2], the central NiII atom is coordinated by two O atoms from two 4-formylbenzoate (FOB) ligands, two O atoms from two water molecules and two N atoms from two diethylnicotinamide (DENA) ligands. The coordination geometry is slightly distorted octahedral, with four O atoms in the equatorial plane and two N atoms in axial positions. Intramolecular O—H⋯O hydrogen bonds are observed. In the crystal structure, molecules are linked into chains along the a axis by intermolecular O—H⋯O hydrogen bonds. The structure is further stabilized by π–π interactions between the pyridine rings of DENA units, with a centroid–centroid distance of 3.668 (2) Å.

In the title centrosymmetric mononuclear Ni II compound, [Ni(C 8 H 5 O 3 ) 2 (C 10 H 14 N 2 O) 2 (H 2 O) 2 ], the central Ni II atom is coordinated by two O atoms from two 4-formylbenzoate (FOB) ligands, two O atoms from two water molecules and two N atoms from two diethylnicotinamide (DENA) ligands. The coordination geometry is slightly distorted octahedral, with four O atoms in the equatorial plane and two N atoms in axial positions. Intramolecular O-HÁ Á ÁO hydrogen bonds are observed. In the crystal structure, molecules are linked into chains along the a axis by intermolecular O-HÁ Á ÁO hydrogen bonds. The structure is further stabilized byinteractions between the pyridine rings of DENA units, with a centroidcentroid distance of 3.668 (2) Å .
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 (Nadzhafov et al., 1981;Shnulin et al., 1981). 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 structure determination of the title compound, a nickel complex with two formylbenzoate (FOB), 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.
The title compound is a monomeric complex, with the Ni II atom on a centre of symmetry (Fig. 1). All ligands are monodentate. The four O atoms (O1, O5, and the symmetry-related atoms, O1′, O5′) lie in the equatorial plane around the Ni1 atom forming a slightly distorted square-planar arrangement, while the slightly distorted octahedral coordination is completed by the two N atoms of the DENA ligands (N1, N1′) in the axial positions (Table 1 and Fig. 1). An intramolecular O-H···O hydrogen bond (Table 2)  In the crystal structure, intermolecular O-H···O hydrogen bonds (Table 1) link the molecules into infinite chains (Fig. 2) along the a axis, which may be effective in the stabilization of the structure. A π-π contact is also observed between the pyridine rings (N1/C9-C13, centroid Cg1) of DENA units, with a Cg1···Cg1 i [symmetry code: (i) 1-x, -1-y, -z] distance of 3.668 (2) Å.

S2. Experimental
The title compound was prepared by the reaction of Ni(SO 4 )H 2 O (1.73 g, 10 mmol) in H 2 O (50 ml) and DENA (3.56 g, 20 mmol) in H 2 O (15 ml) with sodium 4-formylbenzoate (3.44 g, 20 mmol) in H 2 O (50 ml). The mixture was filtered and set aside to crystallize at ambient temperature for several days, giving green single crystals.

S3. Refinement
H atoms of water molecule were located in a difference Fourier map and refined isotropically, with O-H and H···H distances restrained to 0.84 (1) Å and 1.37 (2) Å, respectively. 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 atoms and x = 1.2 for all other H atoms.

Figure 1
The molecular structure of the title compound 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 (-x, -y, -z).

Diaquabis(N,N-diethylnicotinamide-κN 1 )bis(4-formylbenzoato-κO)nickel(II)
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.50 e Å −3 Δρ min = −0.31 e Å −3 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 > 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.