Diaqua[(1R,2S,4R,8R,9S,11R)-2,9-dimethyl-1,4,8,11-tetraazacyclotetradecane]nickel(II) dichloride dihydrate

The crystal structure of the title complex, [Ni(C12H28N4)(H2O)2]Cl2·2H2O, displays O—H⋯Cl and O—H⋯O hydrogen bonding. The tetraazacyclotetradecane ligand interacts with the NiII atom in the cis V configuration and the final two ligand binding sites are occupied by water.


D-HÁ
Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP in SHELXTL (Sheldrick, 2008); software used to prepare material for publication: XCIF in SHELXTL. The ligand in the title compound was synthesized by base-catalyzed metal-templated cyclization of dipeptides, metal removal using HCl and finally amide reduction to yield a C-functionalized cyclam molecule (Beck & Lang, 2003). The stereochemical integrity of the ligands previously synthesized, however, was never established. Strong bases such as NaOMe, which is used in the ligand synthesis, have the ability to racemize peptides Liardon et al. (1986). The crystal structure of the title compound shows that the stereochemical integrity of the (2S,9S)-2,9-dimethyl-1,4,8,11-tetraazacyclotetradecane ligand is maintained throughout the synthesis. Cyclam metal complexes have 6 possible configurations: trans I-V and cis V (Liang et al., 2002). Typically the structure of cyclam metal complexes tends to favor the thermodynamically most stable trans III configuration in the solid state (Liang et al., 2002). However, in this case the compound has adopted the cis V configuration with two water molecules acting as ligands to the metal center. The chloride counter ions interact with the water ligands through O-H···Cl hydrogen bonds. Similarly configured nickel cyclam complexes were reported by Ito et al. (1981Ito et al. ( , 1982. A recent crystal structure search in the CCDC database has shown that only 4% of cyclam complexes without nitrogen functionalization, utilizing halogen containing counter ions and monodentate ligands for the final two coordination sites, adopt a cis V configuration (Allen, 2002).
When chiral carbons are present in the cyclam it is possible to generate two stereoisomers for each metal complex configuration. The diastereomers for each configuration are dependent on the chirality around the N atoms in the complex as the carbon chirality in the cyclam ligand is both encoded and maintained during synthesis. The title compound has adopted a diastereomer that places the methyl side arms into the equatorial plane of the 5 membered rings. This minimizes steric interactions with the remainder of the cyclam and the water ligands attached to the nickel center.

Refinement
All hydrogen atoms, excepting amine and water H atoms, were placed in idealized positions and allowed to ride.
Coordinates of the amine and water H atoms were allowed to refine. Absolute configuration was determined by inspection of the Flack parameter produced by least-squares refinement. A value of -0.006 (7)

Figure 1
The molecular structure of the title compound, showing 50% probability displacement ellipsoids.  (7) Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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.