(2R)-2-Methylpiperazinediium tetrachloridocuprate(II)

In the title compound, (C5H14N2)[CuCl4], the copper(II) ion has a slightly tetrahedrally distorted square-planar coordination geometry and the diprotonated piperazine ring adopts a chair conformation. In the crystal structure, cations and anions are linked by intermolecular N—H⋯Cl hydrogen bonds, forming a three-dimensional network.

In the title compound, (C 5 H 14 N 2 ) [CuCl 4 ], the copper(II) ion has a slightly tetrahedrally distorted square-planar coordination geometry and the diprotonated piperazine ring adopts a chair conformation. In the crystal structure, cations and anions are linked by intermolecular N-HÁ Á ÁCl hydrogen bonds, forming a three-dimensional network.

Comment
The existence of a chiral centre in an organic ligand is very important for the construction noncentrosymmetric or chiral coordination polymers that exhibit desirable physical properties such as ferroelectricity (Fu et al., 2007) and nonlinear optical second harmonic generation (Qu et al., 2003). Chiral (R)-2-methylpiperazine has a chiral centre which have shown tremendous scope in the synthesis of transition metal complexes (Ye et al., 2009). The construction of new members of this family of ligands is an important direction in the development of modern coordination chemistry. We report here the crystal structure of the title compound The asymmetric unit of the title compound consists of a diprotonated (R)-2-methylpiperazine cation and a tetrachlorocuprate anion (Fig. 1). The copper(II) metal centre is in a slightly tetrahedrally distorted square-planar coordination geometry (maximum displacement 0.0252 (18) Å for atom Cl1). The 6-membered piperazine ring adopts a chair conformation, with puckering parameters (Cremer & Pople, 1975) Q = 0.570 (6) Å, θ = 178.6 (6)° and φ = -127.3 (3)°. The crystal structure is stabilized by inter-ion N-H···Cl hydrogen interactions (Table 1) forming a three-dimensional network (Fig. 2).

Experimental
A mixture of (R)-2-methylpiperazine (1 mmol, 0.1 g ), CuCl 2 (1 mmol, 0.136 g) and 10% aqueous HCl (6 ml) were mixed and dissolved in 30 ml water by heating to 353 K (10 minute) forming a clear solution. The reaction mixture was then cooled slowly to room temperature. Single crystals of the title compound suitable for X-ray analysis were formed after 12 days on slow evaporation of the solvent.

Refinement
All H atoms were placed in calculated positions with C-H = 0.93-0.98 Å, N-H = 0.90 Å, and refined using a riding model, with U iso (H) = 1.2U eq (C, N) or 1.5 U eq (C) for methyl H atoms. Fig. 1. The asymmetric unit of the title compound with atom labels. Displacement ellipsoids were drawn at the 30% probability level.

Figures
supplementary materials sup-2 Crystal data (C 5

Special details
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 > σ(F 2 ) is used only for calculating Rfactors(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Cu1 0.82482 (13