Crystal structure of a nickel compound comprising two nickel(II) complexes with different ligand environments: [Ni(tren)(H(2)O)(2)][Ni(H(2)O)(6)](SO(4))(2)

The title compound, di­aqua­[tris­(2-amino­eth­yl)amine]­nickel(II) hexa­aqua­nickel(II) bis­(sulfate), [Ni(C(6)H(18)N(4))(H(2)O)(2)][Ni(H(2)O)(6)](SO(4))(2) or [Ni(tren)(H(2)O)(2)][Ni(H(2)O)(6)](SO(4))(2), consists of two octa­hedral nickel complexes within the same unit cell. These metal complexes are formed from the reaction of [Ni(H(2)O)(6)](SO(4)) and the ligand tris­(2-amino­eth­yl)amine (tren). The crystals of the title compound are purple, different from those of the starting complex [Ni(H(2)O)(6)](SO(4)), which are turquoise. The reaction was performed both in a 1:1 and 1:2 metal–ligand molar ratio, always yielding the co-precipitation of the two types of crystals. The asymmetric unit of the title compound, which crystallizes in the space group Pnma, consists of two half Ni(II) complexes and a sulfate counter-anion. The mononuclear cationic complex [Ni(tren)(H(2)O)(2)](2+) comprises an Ni ion, the tren ligand and two water mol­ecules, while the mononuclear complex [Ni(H(2)O)(6)](2+) consists of another Ni ion surrounded by six coordinated water mol­ecules. The [Ni(tren)(H(2)O)(2)] and [Ni(H(2)O)(6)] subunits are connected to the SO(4) (2−) counter-anions through hydrogen bonding, thus consolidating the crystal structure.