catena-Poly[[diaquabis(4-formylbenzoato-κO 1)nickel(II)]-μ-pyrazine-κ2 N:N′]

In the title polymeric compound, [Ni(C8H5O3)2(C4H4N2)(H2O)2]n, the NiII atom is located on a twofold rotation axis and has a slightly distorted octahedral coordination sphere. In the equatorial plane, it is coordinated by two carboxylate O atoms of two symmetry-related monodentate formylbenzoate anions and by two N atoms of the bridging pyrazine ligand, which is bisected by the twofold rotation axis. The axial positions are occupied by two O atoms of the coordinating water molecules. In the formylbenzoate anion, the carboxylate group is twisted away from the attached benzene ring by 7.0 (6)°, while the benzene and pyrazine rings are oriented at a dihedral angle of 66.2 (3)°. The pyrazine ligands bridge the NiII cations, forming polymeric chains running along the b-axis direction. Intramolecular O—H⋯O hydrogen bonds link the water ligands to the carboxylate O atoms. In the crystal, water–water O—H⋯O hydrogen bonds link adjacent chains into layers parallel to the bc plane. Pyrazine–formyl C—H⋯O hydrogen bonds link the layers, forming a three-dimensional network. There are also weak C—H⋯π interactions present. The title compound is isotypic with the copper(II) complex [Çelik et al. (2014a). Acta Cryst. E70, m4–m5].


Comment
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 . 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). Some benzoic acid derivatives, such as 4-aminobenzoic acid, have been extensively reported in coordination chemistry, as bifunctional organic ligands, due to the varieties of their coordination modes (Chen & Chen, 2002;Amiraslanov et al., 1979;Hauptmann et al., 2000). The title compound, which is isotructural with the copper(II) complex (Çelik et al., 2014a) was synthesized and its crystal structure is reported on herein.
The asymmetric unit of the title compound contains half a Ni II ion, one formylbenzoate (FB) anion, one water molecule and half of a pyrazine molecule. Atoms Ni1, and N1 and N2 of the pyrazine ligand, are located on a two-fold rotation axis ( Fig. 1). The pyrazine ligands bridge adjacent Ni II ions forming polymeric chains running along the b-axis direction (Fig.   2). The distances between the symmetry related Ni II ions [Ni1···Ni1 i ; symmetry code: (i) x, y + 1, z] is 6.992 (3) Å.
In the equatorial plane of the Ni II , coordination sphere is composed of two carboxylate O atoms (O2 and O2 ii ; symmetry code: (ii) -x, y, -z + 1/2) of two symmetry related monodentate formylbenzoate anions and two N atoms (N1 and N2) of the bridging pyrazine ligand, which is bisected by the two-fold rotation axis. The axial positions are occupied by two O atoms (O4 and O4 ii ) of the coordinated water molecules.
In the crystal, O-H water ···O water hydrogen bonds link adjacent chains into layers parallel to the bc plane (Table 1). C-H pyrazine ···O formyl hydrogen bonds (Table 1) link the layers to form a three-dimensional network. There are also weak C-H···π interactions present (Table 1).

Experimental
The title compound was prepared by the reaction of NiSO 4 .6H 2 O (1.31 g, 5 mmol) in H 2 O (70 ml) and pyrazine (0.40 g, 5 mmol) in H 2 O (30 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 one week, giving blue prismatic crystals.

Refinement
Atoms H41 and H42 (for H 2 O) were located in a difference Fourier map and were refined with distance restraints: O-H = 0.82 (2) Å. 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). Both the highest residual electron density and the deepest hole were found 0.88 Å from atom Ni1.

Figure 1
A view of the coordination geometry around the Ni II atom of the title molecule, with the atom-labelling. Displacement ellipsoids are drawn at the 50% probability level. The two-fold rotation axis bisects atoms Ni1, N1 and N2.

catena-Poly[[diaquabis(4-formylbenzoato-κO 1 )nickel(II)]-µ-pyrazine-κ 2 N:N′]
Crystal data [Ni(C 8  Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles 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.