Crystal structure and Hirshfeld surface analysis of a bromochalcone: (E)-1-(3-bromophenyl)-3-(2,6-dichlorophenyl)prop-2-en-1-one

In the title chalcone derivative, C15H9Cl2BrO, the two aryl rings are inclined to each other by 14.49 (17)°, and the olefinic double bond adopts an E configuration. In the crystal, the only short intermolecular contacts are Cl⋯O contacts [3.173 (3) Å] that link the molecules to form a 21 helix propagating along the b-axis direction.


Chemical context
Chalcones, considered to be the precursors of flavonoids and isoflavonoids, are abundant in edible plants. Chemically they consist of open-chain flavonoids in which the two aromatic rings are joined by a three-carbon, -unsaturated carbonyl system and are described by the generic term 'chalcone'. Chalcones are coloured compounds because of the presence of the -CO-CH CH-chromophore, which depends on the presence of other auxochromes. Chalcones are finding applications as organic non-linear optical materials (NLO) because of their good SHG conversion efficiencies (Chandra Shekhara Shetty et al., 2016;Raghavendra et al., 2017). In view of this interest we have synthesized the title chalcone derivative and report herein on its crystal structure and Hirshfeld surface analysis.

Structural commentary
The molecular structure of the title compound is shown in Fig. 1. It comprises two aromatic rings (2,6-dichlorophenyl and ISSN 2056-9890 3-bromophenyl) linked by the C7 C8-C9( O1)-C10 enone bridge. The bond lengths and bond angles are normal and the molecular conformation is characterized by a dihedral angle of 14.49 (17) between the mean planes of the two aromatic rings. The olefinic double bond [C7 C8 = 1.286 (5) Å ] is in an E configuration. There is a short intramolecular C-HÁ Á ÁCl contact present resulting in the formation of an S(6) ring motif ( Fig. 1 and Table 1). The unsaturated keto group is in a syn-periplanar conformation with respect to the olefinic double bond, which is evident from the O1-C9-C8-C7 torsion angle of 10.9 (6) . The trans conformation of the C C double bond in the central enone group is confirmed by the C6-C7-C8 C9 torsion angle of À179.8 (3) . The bond angles O1-C9-C10 [120.4 (3) ], O1-C9-C8 [119.9 (3) ] and C9-C8-C7 [123.9 (4) ] about C9 indicate that this carbon atom is in a distorted trigonal-planar conformation.

Hirshfeld surface analysis
Hirshfeld surfaces and fingerprint plots were generated for the title compound using CrystalExplorer (Wolff et al., 2012). Hirshfeld surfaces enable the visualization of intermolecular interactions by different colours and colour intensity, representing short or long contacts and indicating the relative strength of the interactions.  Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
A partial view along the c axis of the crystal packing of the title compound. The intermolecular ClÁ Á ÁO interactions are shown as dashed lines.

Figure 3
A view along the a axis of the crystal packing of the title compound. The intermolecular ClÁ Á ÁO interactions are shown as dashed lines.

Figure 1
The molecular structure of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 50% probability level. The intramolecular C-HÁ Á ÁCl hydrogen bond (Table 1) is shown as a dashed line.

Synthesis and crystallization
The

Special details
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement on F 2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses 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 observed criterion of F 2 > 2sigma(F 2 ) is used only for calculating -R-factor-obs 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. Geometric parameters (Å, º)