catena-Poly[[[diaqua-(di-2-pyridylamine-κN,N')nickel(II)]-μ-fumarato-κO:O] tetra-hydrate].

In the crystal structure of the title compound, {[Ni(C(4)H(2)O(4))(C(10)H(9)N(3))(H(2)O)(2)]·4H(2)O}(n), zigzag chains are built up from cis-[Ni(dpya)(H(2)O)(2)](2+) cations (dpya is di-2-pyridylamine) linked by bis-monodentate coordinated bridging fumarate ligands. The Ni(II) atom is coordinated by one chelating dpya ligand, two aqua ligands in trans positions and two monodentate fumarate ligands in cis positions in the form of a deformed octa-hedron. The water mol-ecules, O atoms of the fumarate carboxyl-ate groups and the amine group of the dpya ligand are involved in an extended network of intra- and inter-molecular O-H⋯O hydrogen bonds. Moreover, π-π inter-actions between the pyridine rings of the dpya ligand contribute to the stability of the structure. Two of the five uncoordinated water molecules are half-occupied.