Crystal structure of catena-poly[[aqua­bis­(4-formyl­benzoato)-κ(2) O (1),O (1′);κO (1)-zinc]-μ-pyrazine-κ(2) N:N′]

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. Medium-strength intra­molecular O—H⋯O hydrogen bonds link the water mol­ecules to the carboxyl­ate O atoms. In the crystal, 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. 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 inter­actions present.