4,4′,6,6′-Tetrachloro-2,2′-[(1E,1′E)-propane-1,3-diylbis(nitrilomethanylylidene)]diphenol

The title compound, C17H14Cl4N2O2, is generated by crystallographic twofold symmetry. The two benzene rings are inclined to one another by 80.17 (10)°. There are two intramolecular O—H⋯N hydrogen bonds, which make S(6) ring motifs. In the crystal, molecules are linked by C—H⋯O and weak C—H⋯Cl interactions, forming a three-dimensional network.

The title compound, C 17 H 14 Cl 4 N 2 O 2 , is generated by crystallographic twofold symmetry. The two benzene rings are inclined to one another by 80.17 (10) . There are two intramolecular O-HÁ Á ÁN hydrogen bonds, which make S(6) ring motifs. In the crystal, molecules are linked by C-HÁ Á ÁO and weak C-HÁ Á ÁCl interactions, forming a three-dimensional network.
The title compound, Fig. 1, a potential tetradentate Schiff base ligand, possesses two-fold rotation symmetry, atom C9 is located on the 2-fold axis. The bond lengths (Allen et al., 1987) and angles are within the normal ranges. The two symmetry related benzene rings are inclined to one another by 80.17 (10) °. There are two intramolecular O-H···N hydrogen bonds which make S(6) ring motifs (Table 1; Bernstein et al., 1995).
In the crystal, molecules are linked by C-H···O and weak C-H···Cl interactions to form a three-dimensional network (Table 1 and Fig. 2).

Experimental
The title compound was synthesized by adding 3,5-dichlorosalicylaldehyde (2 mmol) to a solution of propylenediamine (1 mmol) in ethanol (30 ml). The mixture was refluxed with stirring for 30 min. The resultant solution was filtered. Lightyellow prismatic single crystals of the title compound, suitable for X-ray structure determination, were recrystallized from ethanol by slow evaporation of the solvents at room temperature over several days.

Refinement
The OH and C-bound H atoms were included in calculated positions and treated as riding atoms: O-H = 0.82 Å, C-H = 0.93 and 0.96 Å, with U iso (H) = k × U eq (O,C) where k = 1.5 for OH and CH 3 H atoms and = 1.2 for other H atoms.

Computing details
Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97   where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.14 e Å −3 Δρ min = −0.16 e Å −3 Absolute structure: Flack (1983), 842 Friedel pairs Flack parameter: 0.08 (7) 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 > 2sigma(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.