catena-Poly[[di-aqua-bis-(4-formyl-benzo-ato-κO (1))nickel(II)]-μ-pyrazine-κ(2) N:N'].

In the title polymeric compound, [Ni(C8H5O3)2(C4H4N2)(H2O)2] n , the Ni(II) atom is located on a twofold rotation axis and has a slightly distorted octa-hedral coordination sphere. In the equatorial plane, it is coordinated by two carboxyl-ate O atoms of two symmetry-related monodentate formyl-benzoate anions and by two N atoms of the bridging pyrazine ligand, which is bis-ected by the twofold rotation axis. The axial positions are occupied by two O atoms of the coordinating water mol-ecules. In the formyl-benzoate anion, the carboxyl-ate 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. Intra-molecular O-H⋯O hydrogen bonds link the water ligands to the carboxyl-ate 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 inter-actions present. The title compound is isotypic with the copper(II) complex [Çelik et al. (2014a). Acta Cryst. E70, m4-m5].