(2E)-1-(4-Bromophenyl)-3-(4-fluorophenyl)prop-2-en-1-one

The title compound, C15H10BrFO, is isostructural with (2E)-1-(4-chlorophenyl)-3-(4-fluorophenyl)prop-2-en-1-one [Qiu et al. (2006 ▶). Acta Cryst. E62, o3525–o3526], but the structures of other dihalogen analogues, without fluorine, are different, although they are also isostructural within the series. The molecule is approximately flat, the dihedral angle between the ring planes being 8.49 (13)°. In the crystal structure, intermolecular C—H⋯O, C—H⋯F and C—H⋯Br hydrogen bonds link molecules into V-shaped ribbons running parallel to [101] and stacked with an interplanar distance of approximately 3.53 Å (centroid–vcentroid distance = 3.857 Å)..

BN thanks the UGC, New Delhi, Government of India, for the purchase of chemicals through the SAP-DRS-Phase 1 programme.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: RZ2439). Siemens (1989

Comment
Chalcones or 1,3-diaryl-2-propen-1-ones (Ar-CH=CH-CO-Ar) are one of the major classes of natural products with widespread distribution in fruits, vegetables, spices, tea and soy based foodstuff. These compounds have been recently subjects of great interest for their interesting pharmacological activities (Dhar, 1981). They are finding application as organic nonlinear optical materials (NLO) for their SHG conversion efficiency (Sarojini et al., 2006). Among several organic compounds reported which have NLO properties, chalcones derivatives are recognized material because of their excellent blue light transmittance and good crystallization ability (Goto et al., 1991;Uchida et al. (1998); Indira et al., 2002).
In the Cambridge Structural Database (Allen, 2002;Version 5.31, Nov. 2009) there are structural data for a series of the The crystal structure of I is isostructural with the F-Cl analogue; both compounds crystallize in the P2 1 /n space group and their crystal packings are almost identical. The isostructurality index (Kálmán et al., 1991), which measures the differences in the positions of the atoms in the respective unit cell, is 0.9%, which is very close to the ideal value of 0.
The molecule of I is approximately planar (Fig. 1), the dihedral angle between the planes of the aromatic rings is 8.49 (13)°, and the central C=C-C=O fragment, is inclined by about 10° with respect to both rings. This conformation is of course similar to the F-Cl analogue, where the terminal planes make a angle of 9.1°, but is essentially different from the other group of halogeno-derivatives, where the conformation is much more folded, the dihedral angles being around 45°. It might be noted that there is also another difference: in the latter structures the angles between the central plane and the ring planes approximately sum up to the value of the angle between terminal planes. That means that in these cases the rings are twisted in opposite directions with respect to the central plane, while in I they are twisted in the same direction.
In the crystal structure, the molecules are connected by means of weak C-H···O hydrogen bonds into centrosymmetric dimers, and these dimers are connected by weak C-H···F interactions into two-molecule wide ribbons (Fig. 2). Neighbouring ribbons, inclined by an angle of approximately 58°, are connected by C-H···Br contacts (Fig. 3). In spite of the compounds without fluorine, there are no short halogen···halogen contacts. This might be regarded as another evidence of the essential difference between fluorine and other halogen atoms.
supplementary materials sup-2 Additionally, thanks to the short unit cell parameter of 4.0060 (5)Å, the planes of molecules are stacked one onto another with an interplanar distance of about 3.53Å.
Experimental 10 ml of 10% KOH was added to a mixture of 4-bromoacetophenone (0.01 mol) and p-fluorobenzaldehyde (0.01 mol) in 40 mL of ethyl alcohol. The reaction mixture was then kept under constant stirring. The solid product was filtered and recrystallized from an ethyl acetate solution at room temperature. C 15 H 10 BrFO, calculated: C 59.04% 3.30%, found: C 58.98, H 3.25. M.P.: 362-366 K.

Refinement
The non-standard setting of space group P21/c (a=4.0060Å, b=23.125Å, c=14.4935Å, β=112.289°; transformation matrix 1 0 0 / 0 1 0 / -1 0 1) was chosen in order to be in accordance with the previously published isostructural structure. Hydrogen atoms were freely refined. Fig. 1. Perspective view of the title compound with labelling scheme and displacement ellipsoids drawn at 50% probability level. Hydrogen atoms are depicted as spheres with arbitrary radii.    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 > 2σ(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.