Crystal structure of catena-poly[[aquabis(4-formylbenzoato)-kappa O-2(1),O1 ';kappa O-1-zinc]-mu-pyrazine-kappa N-2:N ']

The asymmetric unit of the title polymeric compound, [Zn(C8H5O3)(2)(C4H4N2)(H2O)](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)degrees, respectively. In the disordered FB anions, the corresponding angles are 14.1 (1) and 4.0 (2)degrees for benzene rings A and D, respectively. Benzene rings A and B are oriented at a dihedral angle of 45.7 (1)degrees, D and E at 23.2 (1)degrees. Pyrazine ring C makes dihedral angles of 85.6 (1) and 72.7 (1)degrees, respectively, with benzene rings A and B, and pyrazine ring F makes dihedral angles of 87.0 (1) and 81.3 (1)degrees 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. Mediumstrength intramolecular O-H center dot center dot center dot O hydrogen bonds link the water molecules to the carboxylate O atoms. In the crystal, water-carboxylate O-H center dot center dot center dot O hydrogen bonds link adjacent chains into layers parallel to the bc plane. The layers are linked via weak pyrazine-formyl C-H center dot center dot center dot O and formyl-carboxylate C-H center dot center dot center dot O hydrogen bonds. pi-pi contacts between the benzene rings, with centroid-to-centroid distances of 3.7765 (16), 3.7905 (15) and 3.8231 (16) angstrom, may further stabilize the structure. There are also weak C-H center dot center dot center dot pi interactions present.