Crystal structure of catena-poly[[aqua-bis-(4-formyl-benzoato)-κ(2) O (1),O (1');κO (1)-zinc]-μ-pyrazine-κ(2) 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)†à , may further stabilize the structure. There are also weak C-H⋯π inter-actions present.