N,N′-Bis(3-chloro-2-fluorobenzylidene)ethane-1,2-diamine

The molecule of the title centrosymmetric Schiff base compound, C16H12Cl2F2N2, adopts an E configuration with respect to the azomethine C=N bond. The imino groups are coplanar with the aromatic rings. Within the molecule, the planar units are parallel, but extend in opposite directions from the dimethylene bridge. An interesting feature of the crystal structure is the short intermolecular Cl⋯F [3.1747 (5) Å] interactions, which are shorter than the sum of the van der Waals radii of these atoms. These interactions link neighbouring molecules along the b axis. The crystal structure is further stabilized by π–π interactions, with a centroid–centroid distance of 3.5244 (4) Å.

The molecule of the title centrosymmetric Schiff base compound, C 16 H 12 Cl 2 F 2 N 2 , adopts an E configuration with respect to the azomethine C N bond. The imino groups are coplanar with the aromatic rings. Within the molecule, the planar units are parallel, but extend in opposite directions from the dimethylene bridge. An interesting feature of the crystal structure is the short intermolecular ClÁ Á ÁF [3.1747 (5) Å ] interactions, which are shorter than the sum of the van der Waals radii of these atoms. These interactions link neighbouring molecules along the b axis. The crystal structure is further stabilized byinteractions, with a centroid-centroid distance of 3.5244 (4) Å .

N,N'-Bis(3-chloro-2-fluorobenzylidene)ethane-1,2-diamine
H.-K. Fun and R. Kia Comment Schiff bases are among the most prevalent mixed-donor ligands in the field of coordination chemistry in which there has been growing interest, mainly because of their wide application in areas such as biochemistry, synthesis, and catalysis (Pal et al., 2005;Hou et al., 2001;Ren et al., 2002). Many Schiff base complexes have been structurally characterized, but only a relatively small number of free Schiff bases have had their X-ray structures reported (Calligaris & Randaccio, 1987). As an extension of our work (Fun, Kargar & Kia 2008;Fun, Kia & Kargar 2008) on the structural characterization of Schiff base ligands, the title compound (I), is reported here.
The molecule of the title compound ( Fig. 1), adopts an E configuration with respect to the azomethine C═N bond. The bond lengths (Allen et al., 1987) and angles are within normal ranges and are comparable with the values found in related structures (Fun & Kia 2008a,b;Fun, Kargar & Kia 2008;Fun, Kia & Kargar 2008). The two planar units are parallel but extend in opposite directions from the dimethylene bridge. The interesting feature of the crystal structure is the short intermolecular Cl···F interactions [symmetry code: x, -1/2 -y, -1/2 + z] with a distance of 3.1747 (5) Å, which is shorter than the sum of the van der Waals radii of these atoms. These interactions link neighbouring molecules along the b-axis.

Experimental
The synthetic method has been described earlier (Fun, Kargar & Kia, 2008). Single crystals suitable for X-ray diffraction were obtained by evaporation of an ethanol solution at room temperature.

Refinement
All of the hydrogen atoms were positioned geometrically with C-H = 0.95 or 0.99 Å and refined in riding mode with U iso (H) = 1.2 U eq (C). Fig. 1. The molecular structure of (I) with atom labels and 50% probability ellipsoids for non-H atoms. The suffix A corresponds to symmetry code (-x + 2, -y, -z + 1).

Special details
Experimental. The low-temperature data was collected with the Oxford Cyrosystem Cobra low-temperature attachment. 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