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

The asymmetric unit of the title complex salt, [Ni(C10H24N4)(H2O)2](C4H2O4)·4H2O, comprises half of a nickel(II) complex dication, half of a fumarate dianion and two water molecules. Both the NiII cation and fumarate anion lie on a crystallographic inversion center. The NiII ion in the cyclam complex is six-coordinated within a distorted N4O2 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. NiII 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.