μ-Squarato-κO:O-bis-{[2-(2-amino-ethyl)pyridine-κN,N']aqua-nickel(II)} squarate 0.25-hydrate.

The asymmetric unit of title compound, [Ni(2)(C(4)O(4))(C(7)H(10)N(2))(4)(H(2)O)(2)]C(4)O(4)·0.25H(2)O, contains one-half of a squarate ligand, one-half of an uncoordinated squarate dianion, two 2-(2-amino-ethyl)pyridine ligands and one aqua ligand, all coordinated to an Ni(II) ion. The compound also contains 0.25 solvent water mol-ecules. The Ni(II) ion has distorted octa-hedral geometry. The squarate ligand adopts a μ-1,2 coordination mode, the intra-dimer Ni(II)⋯Ni(II) separation being 7.1442 (7) Å, while the other squarate unit acts as a counter-anion. The crystal structure is stabilized by inter-molecular O-H⋯O and N-H⋯O hydrogen-bond inter-actions, forming a three-dimensional network.