Diaquabis(4-methylbenzoato-κO)bis(nicotinamide-κN 1)nickel(II)

The title NiII complex, [Ni(C8H7O2)2(C6H6N2O)2(H2O)2], is centrosymmetric with the Ni atom located on an inversion center. The molecule contains two 4-methylbenzoate (PMB) and two nicotinamide (NA) ligands and two coordinated 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 carboxylate group and the adjacent benzene ring is 26.15 (10)°, while the pyridine and benzene rings are oriented at a dihedral angle of 87.81 (4)°. In the crystal structure, intermolecular O—H⋯O and N—H⋯O hydrogen bonds link the molecules into a three-dimensional network. The π–π contact between the benzene rings [centroid–centroid distance = 3.896 (1) Å] may further stabilize the crystal structure. A weak C—H⋯π interaction involving the pyridine ring also occurs.

In the crystal structure, intermolecular O-H···O and N-H···O hydrogen bonds (Table 2) link the molecules into a three-dimensional network, in which they may be effective in the stabilization of the structure. The π-π contact between the benzene rings, Cg1-Cg1 i , [symmetry code (i): 1 -x, -y, 2 -z, where Cg1 is the centroid of ring A (C2-C7)] may further stabilize the structure, with centroid-centroid distance of 3.896 (1) Å. There also exists a weak C-H···π interaction involving the pyridine ring (Table 2).

Experimental
The title compound was prepared by the reaction of NiSO 4 .6(H 2 O) (1.32 g, 5 mmol) in H 2 O (30 ml) and NA (1.22 g, 10 mmol) in H 2 O (15 ml) with sodium 4-methylbenzoate (1.36 g, 10 mmol) in H 2 O (300 ml). The mixture was filtered and set aside to crystallize at ambient temperature for one week, giving blue single crystals.
supplementary materials sup-2 Refinement Atoms H21, H22 (for NH 2 ) and H41, H42 (for H 2 O) were located in a difference Fourier map and refined isotropically.
The remaining H atoms were positioned geometrically with C-H = 0.93 and 0.96 Å, for aromatic and methyl H atoms, respectively, 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 molecule with the atom-numbering scheme. Displacement ellipsoids are drawn at the 20% probability level. Primed atoms are generated by the symmetry operator:(') -x, -y, 1 -z.

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 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.