Propane-1,2-diammonium bis­(pyridine-2,6-dicarboxyl­ato-κ(3) O,N,O′)nickelate(II) tetra­hydrate

The reaction of nickel(II) nitrate hexa­hydrate, propane-1,2-diamine and pyridine-2,6-dicarboxylic acid in a 1:2:2 molar ratio in aqueous solution resulted in the formation of the title compound, (C(3)H(12)N(2))[Ni(C(7)H(3)NO(4))(2)]·4H(2)O or (p-1,2-daH(2))[Ni(pydc)(2)]·4H(2)O (where p-1,2-da is propane-1,2-diamine and pydcH(2) is pyridine-2,6-dicarboxylic acid). The geometry of the resulting NiN(2)O(4) coordination can be described as distorted octa­hedral. Considerable C=O⋯π stacking inter­actions are observed between the carboxyl­ate C=O groups and the pyridine rings of the (pydc)(2−) fragments, with O⋯π distances of 3.1563 (12) and 3.2523 (12) Å and C=O⋯π angles of 95.14 (8) and 94.64 (8)°. In the crystal structure, a wide range of non-covalent inter­actions, consisting of hydrogen bonding [O—H⋯O, N—H⋯O and C—H⋯O, with D⋯A distances ranging from 2.712 (2) to 3.484 (2) Å], ion pairing, π–π [centroid-to-centroid distance = 3.4825 (8) Å] and C=O⋯π stacking, connect the various components to form a supra­molecular structure.