N,N′-Bis(2,6-dichlorobenzylidene)propane-1,2-diamine

In the title Schiff base, C17H14Cl4N2, the atoms of one of the 2,6-dichlorobenzylidene units and the central 1,2-diaminopropane grouping are disordered over two sets of sites in a 0.8838 (12):0.1162 (12) ratio. The dihedral angles between the ordered benzene ring and its disordered counterparts are 57.41 (12) and 54.8 (6)° for the major and minor disorder components, respectively. The crystal studied was a racemic twin, the refined ratio of the twin components being 0.37 (5):0.63 (5).

In the title Schiff base, C 17 H 14 Cl 4 N 2 , the atoms of one of the 2,6-dichlorobenzylidene units and the central 1,2-diaminopropane grouping are disordered over two sets of sites in a 0.8838 (12):0.1162 (12) ratio. The dihedral angles between the ordered benzene ring and its disordered counterparts are 57.41 (12) and 54.8 (6) for the major and minor disorder components, respectively. The crystal studied was a racemic twin, the refined ratio of the twin components being 0.37 (5):0.63 (5).

Related literature
For background to Schiff bases and their applications, see: Garnovskii et al. (1993); Sreedaran et al. (2008); Lozier et al. (1975); Yeap et al. (2006); Liu et al. (1990). For the stability of the temperature controller used for the data collection, see: Cosier & Glazer (1986 Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009 (Garnovskii et al., 1993). These compounds played important role in the development of coordination chemistry related to catalysis (Sreedaran et al., 2008) enzymatic reactions (Lozier et al., 1975), liquid crystals (Yeap et al., 2006) and ionophores in the construction of many anion or cation-selective electrodes (Liu et al., 1990). The present work is part of a structural study of compounds of Schiff base systems and we report here the structure of the title compound, (I).
The title compound, (I) is disordered over two positions with refined site-occupancies of 0.8838 (12) and 0.1162 (12) ( Fig. 1). The methyl group at the center of the molecule is at different positions in the major and minor components which is C9A and C8B respectively. The dihedral angles between the two benzene rings are 57.41 (12) (major component) and 54.8 (6)° (minor component). In the crystal structure (Fig. 2), the molecules are stacked along the a axis.
Experimental 2,6-Dichlorobenzaldehyde (0.087 g) and 1,2-diaminopropane (0.370 g) in ethanol/water (40 ml) were heated under reflux for 2 h with stirring. The colourless solution was then cooled to room temperature. After a few days of slow evaporation of the solvent, colourless needles of (I) was obtained.

Refinement
Parts of the molecule are disordered over two sets of sites with refined site-occupancies of 0.8838 (12) and 0.1162 (12). The same U ij parameters were used for atom pair C12B/C14B. The minor component was refined isotropically. The C11B-C16B ring was constrained to a regular hexagon with d = 1.39 Å. The crystal studies was a racemic twin, the refined ratio of twin components being 0.37 (5) : 0.63 (5). All hydrogen atoms were positioned geometrically with a riding model with C-H = 0.93-0.97 Å and U iso (H) = 1.2-1.5 U eq (C). The rotating group model was applied for the methyl groups. Fig. 1. The molecular structure of (I) with 50% probability ellipsoids for non-H atoms. All disordered components are shown.

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 > 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.