The reaction of ethane-1,2-diamine (en, C2H8N2), the sodium salt of naphthalene-1,5-disulfonic acid (H2NDS, C10H8O6S2), and nickel sulfate in an aqueous solution resulted in the formation of the title salt, [Ni(C2H8N2)(H2O)4](C10H6O6S2)·2H2O or [Ni(en)(H2O)4](NDS)·2H2O. In the asymmetric unit, one half of an [Ni(en)(H2O)4]2+ cation and one half of an NDS2− anion, and one water molecule of crystallization are present. The Ni2+ cation in the complex is positioned on a twofold rotation axis and exhibits a slight tetragonal distortion of the cis-NiO4N2 octahedron, with an Ni—N bond length of 2.0782 (16) Å, and Ni—O bond lengths of 2.1170 (13) Å and 2.0648 (14) Å. The anion is completed by inversion symmetry. In the extended structure, the cations, anions, and non-coordinating water molecules are connected by intermolecular N—H...O and O—H...O hydrogen bonding, as well as C—H...π interactions, forming a three-dimensional network.
