catena-Poly[[di­aqua­bis­(4-formyl­benzo­ato-κO (1))nickel(II)]-μ-pyrazine-κ(2) N:N′]

In the title polymeric compound, [Ni(C(8)H(5)O(3))(2)(C(4)H(4)N(2))(H(2)O)(2)](n), the Ni(II) atom is located on a twofold rotation axis and has a slightly distorted octa­hedral coordination sphere. In the equatorial plane, it is coordinated by two carboxyl­ate O atoms of two symmetry-related monodentate formyl­benzoate anions and by two N atoms of the bridging pyrazine ligand, which is bis­ected by the twofold rotation axis. The axial positions are occupied by two O atoms of the coordinating water mol­ecules. In the formyl­benzoate anion, the carboxyl­ate group is twisted away from the attached benzene ring by 7.0 (6)°, while the benzene and pyrazine rings are oriented at a dihedral angle of 66.2 (3)°. The pyrazine ligands bridge the Ni(II) cations, forming polymeric chains running along the b-axis direction. Intra­molecular O—H⋯O hydrogen bonds link the water ligands to the carboxyl­ate O atoms. In the crystal, water–water O—H⋯O hydrogen bonds link adjacent chains into layers parallel to the bc plane. Pyrazine–formyl C—H⋯O hydrogen bonds link the layers, forming a three-dimensional network. There are also weak C—H⋯π inter­actions present. The title compound is isotypic with the copper(II) complex [Çelik et al. (2014a). Acta Cryst. E70, m4–m5].