(E)-3-(4-Chlorophenyl)-1-(2,4-dichloro-5-fluorophenyl)prop-2-en-1-one

In the title chalcone derivative, C15H8Cl3FO, the dihedral angle between the two benzene rings is 43.35 (8)°. Weak C—H⋯O and C—H⋯Cl intramolecular interactions involving the enone group generate S(5) and S(6) ring motifs, respectively. In the crystal structure, molecules are linked into antiparallel chains along the a axis. These chains are stacked along the b axis and short Cl⋯F contacts of 3.100 (1) Å link adjacent molecules of the antiparallel chains into dimers.

In the title chalcone derivative, C 15 H 8 Cl 3 FO, the dihedral angle between the two benzene rings is 43.35 (8) . Weak C-HÁ Á ÁO and C-HÁ Á ÁCl intramolecular interactions involving the enone group generate S(5) and S(6) ring motifs, respectively. In the crystal structure, molecules are linked into antiparallel chains along the a axis. These chains are stacked along the b axis and short ClÁ Á ÁF contacts of 3.100 (1) Å link adjacent molecules of the antiparallel chains into dimers.

S1. Comment
In recent years extensive research has been carried out on organic nonlinear optical materials particularly chalcone derivatives due to their high nonlinearity, varied synthesis, and better laser damage resistance as compared to their inorganic counterparts (Agrinskaya et al., 1999;Shivarama Holla et al., 2004;Patil et al., 2006). In view of the importance of these organic materials, the title compound (I) was synthesized and its crystal structure is reported here.
In the structure, weak C9-H9···O1 and C8-H8···Cl2 intramolecular interactions generate S(5) and S(6) ring motifs (Bernstein et al., 1995) (Table 1). In the crystal structure ( Fig. 2), the molecules are linked into anti-parallel chains along the a axis. These chains are stacked along the b-axis and short Cl···F contacts of 3.100 (1) Å link adjacent molecules of the anti-parallel chains into dimers. The crystal is also stabilized by weak C-H···O and C-H···Cl intramolecular interactions (Table 1).

S2. Experimental
The title compound was synthesized by the condensation of 4-chlorobenzaldehyde (0.01 mol) with 2,4-dichloro-5-fluoroacetophenone (0.01 mol) in methanol (60 ml) in the presence of a catalytic amount of sodium hydroxide solution (10 ml, 10%). After stirring for 8 hr, the contents of the flask were poured into ice-cold water (500 ml) and left to stand for 5 hr.
The resulting crude solid was filtered and dried. Colorless block-shaped single crystals of the title compound suitable for x-ray structure determination were recrystallized from acetone.

S3. Refinement
All H atoms were placed in calculated positions with d(C-H) = 0.93 Å, U iso =1.2U eq (C) for CH and aromatic atoms. The highest residual electron density peak is located at 0.67 Å from C4 and the deepest hole is located at 0.54 Å from Cl1.  The asymmetric unit of (I), showing 50% probability displacement ellipsoids and the atomic numbering. Weak intramolecular C-H···O and C-H···Cl interactions are drawn as dashed lines.

Figure 2
The crystal packing of (I), viewed along the b axis showing stacking of anti-parallel chains of molecules approximately along the b axis. Cl···F short contacts and weak C-H···O and C-H···Cl interactions are drawn as dashed lines. Special details Experimental. The low-temperature data was collected with the Oxford Cyrosystem Cobra low-temperature attachment. 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.