Diaqua­(1,4,8,11-tetra­aza­cyclo­tetra­deca­ne)nickel(II) fumarate tetra­hydrate

The asymmetric unit of the title complex salt, [Ni(C(10)H(24)N(4))(H(2)O)(2)](C(4)H(2)O(4))·4H(2)O, comprises half of a nickel(II) complex dication, half of a fumarate dianion and two water mol­ecules. Both the Ni(II) cation and fumarate anion lie on a crystallographic inversion center. The Ni(II) ion in the cyclam complex is six-coordinated within a distorted N(4)O(2) octa­hedral geometry, with the four cyclam N atoms in the equatorial plane and the two water mol­ecules in apical positions. The six-membered metalla ring adopts a chair conformation, whereas the five-membered ring exists in a twisted form. In the crystal packing, inter­molecular O—H⋯O hydrogen bonds between the water molecules and the carboxyl groups of the fumarate anions lead to the formation of layers with R (4) (2)(8) ring motifs. Ni(II) complex cations are sandwiched between two such layers, being held in place by O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds, consolidating a three-dimensional network.