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

In the title complex, [Ni(C8H5O3)2(C6H6N2O)2(H2O)2], the NiII cation is located on an inversion center and is coordinated by two 4-formylbenzoate (FB) anions, two nicotinamide (NA) ligands and two water molecules. The four O atoms in the equatorial plane around the NiII cation 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 23.67 (8)°, while the pyridine and benzene rings are oriented at an angle of 89.04 (4)°. The coordinating water molecule links with the carboxylate group via an O—H⋯O hydrogen bond. In the crystal, N—H⋯O, O—H⋯O and weak C—H⋯O hydrogen bonds link the molecules into a three-dimensional supramolecular network. π–π contacts between benzene rings [centroid–centroid distance = 3.8414 (7) Å] may further stabilize the structure. A weak C—H⋯π interaction also occurs.

The asymmetric unit of the title mononuclear Ni II complex, (Fig. 1 et al., 2009b) have also been reported. In the copper(II) complex mentioned above the two benzoate ions coordinate to the Cu II atom as bidentate ligands, while in the other structures all the ligands coordinate in a monodentate manner.
In the title complex, the four symmetry related O atoms (O1, O1′, O5 and O5′) 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 the two symmetry related N atoms of the NA ligands (N1 and N1′) in the axial positions. The near equalities of the C1 -O1 [1.2603 (13) Å] and C1-O2 [1.2594 (13) Å] bonds in the carboxylate group indicate delocalized bonding arrangement, rather than localized single and double bonds. The Ni-O bond lengths are 2.0650 (8) Å (for benzoate oxygens) and 2.0879 (8) Å (for water oxygens), and the Ni-N bond length is 2.0773 (9) Å, close to standard values (Allen et al., 1987). The Ni atom is displaced out of the mean-plane of the carboxylate group (O1/C1/O2) by -0.5451 (1) Å. The dihedral angle between the planar carboxylate group and the adjacent benzene ring A (C2-C7) is 23.67 (8)°. The benzene A (C2-C7) and the pyridine B (N1/C9-C13) rings are oriented at a dihedral angle of A/B = 89.04 (4)°.
In the crystal, intermolecular N-H···O, O-H···O and weak C-H···O hydrogen bonds (Table 1) link the molecules into a three-dimensional supramolecular 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, 1 -y, 2 -z, where Cg1 is the centroid of the ring A (C2-C7)] may further stabilize the structure, with centroid-centroid distance of 3.8414 (7) Å]. A weak C-H···π interaction is also found in the crystal structure.

Experimental
The title compound was prepared by the reaction of NiSO 4 .6H 2 O (1.31 g, 5 mmol) in H 2 O (25 ml) and NA (1.22 g, 10 mmol) in H 2 O (50 ml) with sodium 4-formylbenzoate (1.72 g, 10 mmol) in H 2 O (100 ml) at room temperature. The mixture was filtered and set aside to crystallize at ambient temperature for several days, giving blue single crystals.

Refinement
Atoms H8 (for CH), H21 and H22 (for NH 2 ) and H51 and H52 (for H 2 O) were located in a difference Fourier map and were refined freely. The C-bound 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).

Figure 1
The molecular structure of the title molecule with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level [symmetry code: (′) -x, -y, -z].

Diaquabis(4-formylbenzoato-κO 1 )bis(nicotinamide-κN 1 )nickel(II)
Crystal data 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.