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

The asymmetric unit of the title polymeric compound, [Zn(C8H5O3)2(C4H4N2)(H2O)] n , contains two mol-ecular units. Each unit comprises two 4-formyl-benzoate (FB) anions, one pyrazine mol-ecule and one coordinating water mol-ecule; 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 carboxyl-ate 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. Medium-strength intra-molecular O-H⋯O hydrogen bonds link the water mol-ecules to the carboxyl-ate O atoms. In the crystal, water-carboxyl-ate 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 form-yl-carboxyl-ate C-H⋯O hydrogen bonds. π-π contacts between the benzene rings, with centroid-to-centroid distances of 3.7765 (16), 3.7905 (15) and 3.8231 (16) Å, may further stabilize the structure. There are also weak C-H⋯π inter-actions present.