Tetraaqua(2,2′-bipyridine-5,5′-dicarboxylato-κ2N,N′)nickel(II) dihydrate

In the title compound, [Ni(C12H6N2O4)(H2O)(4)]center dot 2H(2)O, obtained from a basic solution of 2,2'-bipyridine-5,5'-dicarboxylate and nickel(II) chloride in water, the central Ni(II) cation (site symmetry 2) is coordinated by two N atoms from the 2,2'-bipyridine-5,5'-dicarboxylate ligand and four aqua O atoms. The N-Ni-N angle is 78.64 (8)degrees. Weak but significant pi-pi stacking interactions exist between the pyridine rings with a centroid-centroid distance of 3.652 (8) angstrom. In addition, four O atoms of the two carboxyl groups form hydrogen bonds with both coordinated and uncoordinated water molecules, forming an infinite three-dimensional network.