{5-Chloro-2-[(4-chlorobenzylidene)amino]phenyl}(phenyl)methanone

In the title compound, C20H13Cl2NO, the C=N bond adopts an E conformation. The chloro-substituted rings form a dihedral angle of 11.99 (9)° with each other and form dihedral angles of 74.95 (9) and 83.26 (10)° with the unsubstituted ring. In the crystal, molecules are connected into dimers by pairs of weak C—H⋯O hydrogen bonds and the dimers are arranged in columns parallel to the a axis.

In the title compound, C 20 H 13 Cl 2 NO, the C N bond adopts an E conformation. The chloro-substituted rings form a dihedral angle of 11.99 (9) with each other and form dihedral angles of 74.95 (9) and 83.26 (10) with the unsubstituted ring. In the crystal, molecules are connected into dimers by pairs of weak C-HÁ Á ÁO hydrogen bonds and the dimers are arranged in columns parallel to the a axis.

Related literature
For the biological activities of Schiff base compounds, see: Solomon & Lowery (1993 Table 1 Hydrogen-bond geometry (Å , ).   Table 1) and arranged in columns parallel to the a axis.

Experimental
The synthesis of title compound was carried out by refluxing a mixture of 4-chlorobenzaldehyde (1 mol) and 2-amino-5chlorobenzophenone (1 mol) in ethanol (50 ml) along with 3 drops of conc. H 2 SO 4 for 5 h at 343 K. After cooling, the mixture was concentrated to one third under reduced pressure. The concentrated reaction mixture was kept at room temperature and yellow crystals were obtained after nine days. The crystalline product was collected, washed with methanol and dried to afford the title compound in 85% yield. Slow evaporation of a methanol solution afforded yellow crystals which were suitable for single-crystal X-ray diffraction studies. All chemicals were purchased from Sigma-Aldrich.

Refinement
H atoms were positioned geometrically with C-H = 0.93 Å, and constrained to ride on their parent atoms with U iso (H)= 1.2U eq (CH).  The molecular structure of (I) with displacement ellipsoids drawn at 30% probability level.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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.