μ-Squarato-κ2O1:O2-bis{[2-(2-aminoethyl)pyridine-κ2N,N′]aquanickel(II)} squarate 0.25-hydrate

The asymmetric unit of title compound, [Ni2(C4O4)(C7H10N2)4(H2O)2]C4O4·0.25H2O, contains one-half of a squarate ligand, one-half of an uncoordinated squarate dianion, two 2-(2-aminoethyl)pyridine ligands and one aqua ligand, all coordinated to an NiII ion. The compound also contains 0.25 solvent water molecules. The NiII ion has distorted octahedral geometry. The squarate ligand adopts a μ-1,2 coordination mode, the intradimer NiII...NiII separation being 7.1442 (7) , while the other squarate unit acts as a counter-anion. The crystal structure is stabilized by intermolecular O—H...O and N—H...O hydrogen-bond interactions, forming a three-dimensional network.