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

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′, 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 Cd(II) cations, forming polymeric chains running along the b-axis direction. In the crystal, O—H(water) ⋯ O(carboxyl­ate) hydrogen bonds link adjacent chains into layers parallel to the bc plane. These layers are linked via C—H(pyrazine) ⋯ O(form­yl) 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.