catena-Poly[[aquabis(4-formylbenzoato-κ2 O 1,O 1′)cadmium]-μ-pyrazine-κ2 N:N′]

The polymeric title compound, [Cd(C8H5O3)2(C4H4N2)(H2O)]n, contains two 4-formylbenzoate (FB) anions, one pyrazine molecule and one coordinating water molecule; the FB anions act as bidentate ligands. The O atom, the aldehyde H atom and the benzene ring of one of the FB anions are disordered over two positions. The O atoms were freely refined [refined occupancy ratio 0.79 (2):0.21 (2)], while the aldehyde H atoms and the benzene ring atoms were refined with fixed occupancy ratios of 0.8:0.2 and 0.5:0.5, respectively. In the ordered FB anion, the carboxylate group is twisted away from the attached benzene ring (A) by 22.7 (8)°. In the disordered FB anion, the corresponding angles are 15.6 (10) and 11.4 (11)° for rings B and B′, respectively. Benzene rings A and B are oriented at a dihedral angle of 24.2 (7), A and B′ at 43.0 (8)°. The pyrazine ring makes dihedral angles of 67.5 (4), 89.6 (7) and 86.2 (7)°, respectively, with benzene rings A, B and B′. The pyrazine ligands bridge the CdII cations, forming polymeric chains running along the b-axis direction. In the crystal, O—Hwater ⋯ Ocarboxylate hydrogen bonds link adjacent chains into layers parallel to the bc plane. These layers are linked via C—Hpyrazine ⋯ Oformyl hydrogen bonds, forming a three-dimensional network. π–π interactions [centroid–centroid distances = 3.870 (11)–3.951 (5) Å] further stabilize the crystal structure. There is also a weak C—H⋯π interaction present.

The polymeric title compound, [Cd(C 8 H 5 O 3 ) 2 (C 4 H 4 N 2 )-(H 2 O)] n , contains two 4-formylbenzoate (FB) anions, one pyrazine molecule and one coordinating water molecule; the FB anions act as bidentate ligands. The O atom, the aldehyde H atom and the benzene ring of one of the FB anions are disordered over two positions. The O atoms were freely refined [refined occupancy ratio 0.79 (2):0.21 (2)], while the aldehyde H atoms and the benzene ring atoms were refined with fixed occupancy ratios of 0.8:0.2 and 0.5:0.5, respectively. In the ordered FB anion, the carboxylate group is twisted away from the attached benzene ring (A) by 22.7 (8) . In the disordered FB anion, the corresponding angles are 15.6 (10) and 11.4 (11) for rings B and B 0 , respectively. Benzene rings A and B are oriented at a dihedral angle of 24.2 (7), A and B 0 at 43.0 (8) . The pyrazine ring makes dihedral angles of 67.5 (4), 89.6 (7) and 86.2 (7) , respectively, with benzene rings A, B and B 0 . The pyrazine ligands bridge the Cd II cations, forming polymeric chains running along the b-axis direction. In the crystal, O-H water Á Á Á O carboxylate hydrogen bonds link adjacent chains into layers parallel to the bc plane. These layers are linked via C-H pyrazine Á Á Á O formyl hydrogen bonds, forming a three-dimensional network.interactions [centroidcentroid distances = 3.870 (11)-3.951 (5) Å ] further stabilize the crystal structure. There is also a weak C-HÁ Á Á interaction present.

Related literature
For structural functions and coordination relationships of the arylcarboxylate ion in transition metal complexes of benzoic acid derivatives, see: Nadzhafov et al. (1981); Shnulin et al. (1981). For applications of transition metal complexes with biochemical molecules in biological systems, see: 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, see: Chen & Chen (2002) Table 1 Hydrogen-bond geometry (Å , ).

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 (Nadzhafov et al., 1981;Shnulin et al., 1981). 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 was synthesized and its crystal structure is reported on herein.
The asymmetric unit of the title polymeric compound contains one Cd II ion, two 4-formylbenzoate (FB) anions, one pyrazine molecule and one coordinated water molecule; the FB anions act as bidentate ligands (Fig. 1). The pyrazine ligands bridge the adjacent Cd II ions forming polymeric chains running along the b-axis direction (Fig. 2). The distances between the symmetry related Cd II ions [Cd1 ···Cd1 i ; symmetry code (i) = x, y + 1, z] is 7.495 (3) Å.
In the crystal, O-H water ··· O carboxylate hydrogen bonds (Table 1) link adjacent chains into layers parallel to the bc plane. The layers are linked via C-H pyrazine ··· O formyl hydrogen bonds (Table 1), forming a three-dimensional network.

Refinement
Atoms H71 and H72 (for H 2 O) were located in a difference and refined with a distance restraint: 0-H = 0.82 (2)   Part of the polymeric chain of the title compound. Only the water H atoms and the major components of the disordered aldehyde and benzene ring are shown.

catena-Poly[[aquabis(4-formylbenzoato-κ 2 O 1 ,O 1′ )cadmium]-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.