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

In the mononuclear NiII title complex, [Ni(C7H4FO2)2(C6H6N2O)2(H2O)2], the NiII atom, located on an inversion center, is coordinated by two nicotinamide and two 4-fluorobenzoate ligands and two water molecules in a distorted N2O4 octahedral geometry. The dihedral angle between the carboxylate group and the adjacent benzene ring is 8.95 (8)°, while the pyridine ring and the benzene ring are oriented at a dihedral angle of 75.01 (7)°. The water molecule links the adjacent carboxylate O atom via an intramolecular O—H⋯O hydrogen bond. In the crystal, O—H⋯O, N—H⋯O, C—H⋯O and C—H⋯F hydrogen bonds link the molecules into a three-dimensional network. π–π stacking between parallel pyridine rings [centroid–centroid distance = 3.7287 (11) Å] is also observed.

In the mononuclear Ni II title complex, [Ni(C 7 H 4 FO 2 ) 2 (C 6 H 6-N 2 O) 2 (H 2 O) 2 ], the Ni II atom, located on an inversion center, is coordinated by two nicotinamide and two 4-fluorobenzoate ligands and two water molecules in a distorted N 2 O 4 octahedral geometry. The dihedral angle between the carboxylate group and the adjacent benzene ring is 8.95 (8) , while the pyridine ring and the benzene ring are oriented at a dihedral angle of 75.01 (7) . The water molecule links the adjacent carboxylate O atom via an intramolecular O-HÁ Á ÁO hydrogen bond. In the crystal, O-HÁ Á ÁO, N-HÁ Á ÁO, C-HÁ Á ÁO and C-HÁ Á ÁF hydrogen bonds link the molecules into a three-dimensional network.stacking between parallel pyridine rings [centroid-centroid distance = 3.7287 (11) Å ] is also observed.
The asymmetric unit of the title mononuclear Ni II complex, (Fig. 1), contains one-half molecule, the Ni II atom being located on an inversion center. It consists of two nicotinamide (NA), two 4-fluorobenzoate (PFB) ligands and two coordinated water molecules, all ligands coordinating in a monodentate manner. The crystal structures of similar omplexes of Cu II , Co II , Ni II , Mn II and Zn II ions, [Cu(C 7 H 5 O 2 ) 2 (C 10 H 14 N 2 O) 2 ] (Hökelek et al., 1996), 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', O4 and O4') 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 N atoms of the NA ligands (N1 and N1') in the axial positions. The near equalities of the C1-O1 [1.2695 (18) Å] and C1-O2 [1.2560 (16) Å] bonds in the carboxylate groups indicate delocalized bonding arrangements, rather than localized single and double bonds. The Ni-O bond lengths are 2.0500 (9) Å (for benzoate oxygen) and 2.0872 (10) Å (for water oxygen), and the Ni-N bond length is 2.1033 (13) Å, close to standard values (Allen et al., 1987). The intramolecular O-H···O hydrogen bonds (Table 1)  In the crystal, intermolecular O-H···O, N-H···O, C-H···O and C-H···F hydrogen bonds (Table 1) link the molecules into a three-dimensional network. There also exists a π-π contact between the pyridine rings, Cg2-Cg2 i , may further stabilize the structure [centroid-centroid distance = 3.729 (1) Å; symmetry code: (i) 2 -x, -y, 1 -z; Cg2 is the centroid of was filtered and set aside to crystallize at ambient temperature for two weeks, giving blue single crystals.

Refinement
Atoms H41 and H42 (for water molecules) and H21 and H22 (for NH 2 groups) were located in a difference Fourier map and were freely refined. 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). Fig. 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, 1-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 > 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.