Synthesis, crystal structure and Hirshfeld surface analysis of di­aqua­bis­(o-phenyl­enedi­amine-κ(2) N,N′)nickel(II) naphthalene-1,5-di­sulfonate

The reaction of o-phenyl­enedi­amine (OPD), sodium naphthalene1,5-di­sulfonate (Na(2)NDS) and nickel sulfate in an ethanol–water mixture yielded the title compound, [Ni(OPD)(2)(H(2)O)(2)]·NDS or [Ni(C(6)H(8)N(2))(2)(H(2)O)(2)](C(10)H(6)O(6)S(2)). This salt consists of a complex [Ni(OPD)(2)(H(2)O)(2)](2+) cation with two bidentate OPD ligands and trans aqua ligands, and a non-coordinating NDS(2–) anion, which is the double-deprotonated form of H(2)NDS. The Ni(II) atom is situated at a center of inversion and exhibits a slightly tetra­gonally distorted {O(2)N(4)} octa­hedral coordination environment, with four shorter equatorial Ni—N bonds [2.0775 (17) and 2.0924 (18) Å] and a longer axial Ni—O bond [2.1381 (17) Å]. The OPD ligand is located about an inversion center and is nearly coplanar with the NiN(4) plane [dihedral angle 0.95 (9)°]. In the crystal, the cations and anions are connected by charge-assisted inter­molecular N—H⋯O and O—H⋯O hydrogen-bonding inter­actions into the tri-periodic network structure. Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from H⋯H (44.1%), O⋯H/H⋯O (34.3%), C⋯H/H⋯C (14.8%) C⋯C (6.5%) (involving the cations) and O⋯H/H⋯O (50%), H⋯H (25%), C⋯H/H⋯C (15.3%), C⋯C (8.2%) (involving the anions) inter­actions.