A second monoclinic polymorph of di-μ-chlorido-bis(chlorido{2-[(4-ethylphenyl)iminomethyl]pyridine-κ2 N,N′}copper(II))

The title compound, [Cu2Cl4(C14H14N2)2], is a new polymorph of a previously reported compound [Dehghanpour et al. (2011 ▶). Acta Cryst. E67, m1296]. The current polymorph was obtained from an acetonitrile solution of the title compound. Like the first polymorph, it is monoclinic (space group P21/c). The unique CuII ion in the title centrosymmetric dinuclear complex is in a distorted trigonal–bipyramidal coordination environment formed by the bis-chelating N-heterocyclic ligand, two bridging Cl ligands and one terminal Cl ligand. In the crystal, weak C—H⋯Cl hydrogen bonds are observed in addition to π–π stacking interactions, with a centroid–centroid distance of 3.6597 (18) Å.

The title compound, [Cu 2 Cl 4 (C 14 H 14 N 2 ) 2 ], is a new polymorph of a previously reported compound . Acta Cryst. E67, m1296]. The current polymorph was obtained from an acetonitrile solution of the title compound. Like the first polymorph, it is monoclinic (space group P2 1 /c). The unique Cu II ion in the title centrosymmetric dinuclear complex is in a distorted trigonal-bipyramidal coordination environment formed by the bis-chelating N-heterocyclic ligand, two bridging Cl ligands and one terminal Cl ligand. In the crystal, weak C-HÁ Á ÁCl hydrogen bonds are observed in addition tostacking interactions, with a centroidcentroid distance of 3.6597 (18) Å .

Experimental
The title complex is shown in Fig. 1. The most significant structural difference between this structure and the polymorph  is the coordination environment of the Cu II ion. The structural index τ, (Addison et al., 1984) which is a measure of trigonal distortion, is 0.75 for the title structure indicating a distorted trigonalbipyramidal environment of Cu(II) for the title compound. The value of τ is 0.21 for the other polymorph with a distorted square-planar coordination enviroment. These differences are shown in Fig. 2.
The interplanar angles between the benzene and pyridine rings in the title structure is 12.40 (15)° whereas this angle is 43.02 (13)° in the polymorph determined by Dehghanpour et al. (2011).

Experimental
The title complex was prepared by the reaction of CuCl 2 (13.4 mg, 0.1 mmol) and (4-methylphenyl)pyridin-2-ylmethyleneamine (21.0 mg, 0.1) in 15 ml of acetonitrile at room temperature. The solution was allowed to stand at room temperature and orange block-shaped crystal of the title compound suitable for X-ray analysis precipitated within few days.

Refinement
All the H atoms were located in the difference electron density map. Nevertheless, the H atoms were constrained and refined in the riding motion approximation: C aryl -H = 0.95, C methylene -H = 0.99, C methyl -H = 0.98 Å. U iso (H aryl/methylene ) = 1.2 × U eq (C carrier ) and U iso (H methyl ) = 1.5 × U eq (C carrier ).

and
Mercury (Macrae et al., 2006); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).   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 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.