catena-Poly[[aquabis(4-formylbenzoato-kappa O-2(1),O-1 ')cadmium]-mu-pyrazine-kappa N-2: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)degrees. In the disordered FB anion, the corresponding angles are 15.6 (10) and 11.4 (11)degrees 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)degrees. The pyrazine ring makes dihedral angles of 67.5 (4), 89.6 (7) and 86.2 (7)degrees, 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 center dot center dot center dot O-carboxylate hydrogen bonds link adjacent chains into layers parallel to the bc plane. These layers are linked via C-H-pyrazine center dot center dot center dot O-formyl hydrogen bonds, forming a three-dimensional network. pi-pi interactions [centroid-centroid distances = 3.870 (11)-3.951 (5) angstrom] further stabilize the crystal structure. There is also a weak C-H center dot center dot center dot interaction present.