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.


Comment
The antiviral properties of cyclam (1,4,8,11-tetraazacyclotetradecane) have stimulated interest in metal complexes of this ligand (Kim et al., 2006). Besides its antiviral property, [Ni(cyclam)(OAc) 2 ] also has protein recognition potential (Hunter et al., 2006). Amongst the metal ions investigated, coordination of Ni II to cyclam rings bridged by 1,4-dimethylene(phenylene) was reported to result in greatest enhancement of its antiviral property (Gerlach et al., 2003). However, the rate of complexation of Ni II to cyclam is the poorest compared to Cu II , Zn II and Co II (Paisey et al., 2004). In this paper, we report the crystal structure of the title compound, obtained by the reaction of a nickel(II) salt, cyclam and sodium fumarate.
The title compound, Fig. 1, consists of one nickel(II) complex cation, one fumarate anion and four water molecules.
In the crystal packing ( Fig. 2), intermolecular O water -H···O carboxylate , hydrogen bonds (Table 1) link with the carboxyl groups of the fumarate anions into a two-dimensional layers with R 2 4 (8) ring motifs (Bernstein et al., 1995). The Ni II complex cations are linked to these layers by O aquo -H···O water , N amine -H···O water , C3-H3B···O carboxylate hydrogen bonds (Table 1) to form a three-dimensional network.

Experimental
Nickel chloride hexahydrate (0.24 g, 1 mmol), cyclam (0.22 g, 1 mmol) and sodium fumarate (0.16 g, 1 mmol) were dissolved in water and heated overnight in a water bath at 313 K. Purple crystals were obtained from the yellow solution.  Fig. 1. The molecular structure of the title complex, showing 50% probability displacement ellipsoids and the atom-numbering scheme. Symmetry-related atoms of the Ni II complex ion and fumarate anion are generated by the symmetry codes -x+2, -y+1, -z and -x+1, -y, -z+1, respectively.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.