Crystal structure of catena-poly[[aquabis(4-formylbenzoato)-κ2 O 1,O 1′;κO 1-zinc]-μ-pyrazine-κ2 N:N′]

In the compound, [Zn(C8H5O3)2(C4H4N2)(H2O)]n, the pyrazine ligands bridge the ZnII cations, forming polymeric chains running parallel to the b-axis direction. Water–carboxylate O—H⋯O hydrogen bonds link adjacent chains into layers parallel to the bc plane. The layers are linked via weak pyrazine–formyl C—H⋯O and formyl–carboxylate C—H⋯O hydrogen bonds.

The asymmetric unit of the title polymeric compound, [Zn(C 8 H 5 O 3 ) 2 (C 4 H 4 N 2 )(H 2 O)] n , contains two molecular units. Each unit comprises two 4-formylbenzoate (FB) anions, one pyrazine molecule and one coordinating water molecule; the FB anions act either as bidentate or as monodentate ligands. The O atoms of the bidentately coordinating FB anions are disordered over two positions, and they were refined with fixed occupancy ratios of 0.75:0.25 and 0.70:0.30, respectively. In the ordered monodentately coordinating FB anions, the carboxylate groups are twisted away from the attached benzene rings (B and E) by 12.1 (2) and 9.2 (2) , respectively. In the disordered FB anions, the corresponding angles are 14.1 (1) and 4.0 (2) for benzene rings A and D, respectively. Benzene rings A and B are oriented at a dihedral angle of 45.7 (1) , D and E at 23.2 (1) . Pyrazine ring C makes dihedral angles of 85.6 (1) and 72.7 (1) , respectively, with benzene rings A and B, and pyrazine ring F makes dihedral angles of 87.0 (1) and 81.3 (1) with benzene rings D and E, respectively. The pyrazine ligands bridge the Zn II cations, forming polymeric chains running parallel to the b-axis direction. Mediumstrength intramolecular O-HÁ Á ÁO hydrogen bonds link the water molecules to the carboxylate O atoms. In the crystal, water-carboxylate O-HÁ Á ÁO hydrogen bonds link adjacent chains into layers parallel to the bc plane. The layers are linked via weak pyrazine-formyl C-HÁ Á ÁO and formyl-carboxylate C-HÁ Á ÁO hydrogen bonds.contacts between the benzene rings, with centroid-tocentroid distances of 3.7765 (16), 3.7905 (15) and 3.8231 (16) Å , may further stabilize the structure. There are also weak C-HÁ Á Á interactions present.

Chemical context
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 (Adiwidjaja et al., 1978;Antsyshkina et al., 1980;Nadzhafov et al., 1981;Shnulin et al., 1981). Transition metal complexes with biochemically active ligands frequently show interesting physical and/or chemical properties, and 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 studied in coordination chemistry as bifunctional organic ligands due to their different coordination modes (Chen & Chen, 2002;Amiraslanov et al., 1979;Hauptmann et al., 2000).
In this context, we report the synthesis and crystal structure of the title compound, [Zn(C 8 H 5 O 3 ) 2 (C 4 H 4 N 2 )(H 2 O)] n , which is closely related to its Cd analogue (Ç elik et al., 2014). In The asymmetric unit of the title compound, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms have been omitted for clarity and only the major occupancy components of the disordered carboxylate O atoms are shown.

Figure 2
A partial view of the crystal packing of the title compound. H atoms have been omitted for clarity.

Figure 3
Part of the crystal structure. Intermolecular water-carboxylate O-HÁ Á ÁO hydrogen bonds are shown as dashed lines. H atoms not involved in hydrogen bonds have been omitted for clarity.

Figure 4
Part of the supramolecular structure formed by the intermolecular watercarboxylate O-HÁ Á ÁO, pyrazine-formyl C-HÁ Á ÁO and formylcarboxylate C-HÁ Á ÁO hydrogen bonds. Hydrogen bonds are shown as dashed lines. H atoms not involved in hydrogen bonds have been omitted for clarity.

Synthesis and crystallization
The title compound was prepared by the reaction of ZnSO 4 ÁH 2 O (0.90 g, 5 mmol) in H 2 O (25 ml) and pyrazine (0.40 g, 5 mmol) in H 2 O (25 ml) with sodium 4-formylbenzoate (1.72 g, 10 mmol) in H 2 O (70 ml). The mixture was filtered and set aside to crystallize at ambient temperature for one week, giving colorless single crystals.

catena-Poly[[aquabis(4-formylbenzoato)-κ 2 O 1 ,O 1′ ;κO 1 -zinc]-µ-pyrazine-κ 2 N:N′]
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.