4,6-Dichloro-2-((E)-{4-[(E)-3,5-dichloro-2-hydroxybenzylideneamino]butylimino}methyl)phenol

The asymmetric unit of the title compound, C18H16Cl4N2O2, comprises half of a potentially tetradentate Schiff base ligand. It is located about a twofold rotation axis that bisects the central C—C bond of the butane-1,4-diamine group. There are two intramolecular O—H⋯N hydrogen bonds making S(6) ring motifs. In the crystal, molecules are linked by pairs of weak C—H⋯Cl interactions, forming inversion dimers, which are further connected by C—H⋯O hydrogen bonds into two-dimensional frameworks that lie parallel to (001).

Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2005)'; data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009  In continuation of our work on the crystal structure analyses of Schiff base ligands (Kargar et al., (2011);Kia et al., (2010), we report herein on the crystal structure of the title compound. The asymmetric unit of the title compound, Fig. 1, comprises half of a potentially tetradentate Schiff base ligand. It is located about a two-fold rotation axis that bisects the central C9-C9a bond of the butane-1,4-diamine group. The bond lengths (Allen et al., 1987) and angles are within the normal ranges. The intramolecular O-H···N hydrogen bonds make S(6) ring motifs ( Fig. 2 and Table 1; Bernstein et al., 1995).
In the crystal, molecules are linked by pairs of weak C-H···Cl interactions to form inversion dimers which are further connected by C-H···O hydrogen bonds along the b axis direction, forming two dimensional networks that lie parallel to the ab plane (Table 1 and Fig. 2).

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

Refinement
The OH H atom was located in a difference Fourier map and was constrained to ride on the parent O atom with U iso (H) = 1.5U eq (O). The C-bound H-atoms were included in calculated positions and treated as riding atoms: C-H = 0.93 and 0.97 Å for CH and CH 2 H-atoms, respectively, with U iso (H) = 1.2U eq (C).

Figure 2
The crystal packing of the title compound showing the C-H···O and weak C-H···Cl interactions (dashed lines; see Table 1 for details) forming two dimensional networks. Only the H atoms involved in hydrogen bonding are shown. 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.