Crystal structure and Hirshfeld surface analysis of a chalcone derivative: (E)-3-(4-fluorophenyl)-1-(4-nitrophenyl)prop-2-en-1-one

The molecular structure of the title chalcone derivative is nearly planar and the molecule adopts a trans-configuration with respect to the conjugated C=C double bond. In the crystal, the molecules are connected by weak intermolecular C—H⋯O and C—H⋯F hydrogen bonds into sheets parallel to (104). Weak intermolecular π–π interactions also occur.

The molecular structure of the title chalcone derivative, C 15 H 10 FNO 3 , is nearly planar and the molecule adopts a trans configuration with respect to the C C double bond. The nitro group is nearly coplanar with the attached benzene ring, which is nearly parallel to the second benzene ring. In the crystal, molecules are connected by pairs of weak intermolecular C-HÁ Á ÁO hydrogen bonds into inversion dimers. The dimers are further linked by another C-HÁ Á ÁO hydrogen bond and a C-HÁ Á ÁF hydrogen bond into sheets parallel to (104).interactions occur between the sheets, with a centroid-centroid distance of 3.8860 (11) Å . Hirshfeld surface analysis was used to investigate and quantify the intermolecular interactions.

Chemical context
Non-linear optics (NLO) is the study of interactions between intense light and matter, in which the dielectric polarization responds non-linearly to the electric field of the light. This non-linearity leads to frequency-mixing processes (second-, third-and high-harmonic generations), the optical Kerr effect etc (Boulanger & Zyss, 2006). Chalcone is one of the NLO materials and is known for its high NLO coefficients and good crystallizability (Prabhu et al., 2013). Donor-acceptor substituted chalcone derivatives consist of two substituted phenyl rings covalently bonded to the ends of a ,-unsaturated propenone bridge (C C-C O), which provides the necessary configuration for intramolecular charge transfer to show NLO properties (Fun et al., 2011). However, organic chalcone derivatives with a low melting point are at a disadvantage for applications as optical instruments. In a continuation of our ongoing studies on non-linear optical properties of various chalcone derivatives (Chandra Shekhara Shetty et al., 2017;Ekbote et al., 2017;Kwong et al., 2018), we report herein the synthesis, structure determination and Hirshfeld surface analysis of the title compound.

Structural commentary
The asymmetric unit of the title chalcone derivative consists of a unique molecule, containing two para-substituted phenyl rings and an enone connecting bridge (Fig. 1). The molecule adopts a trans configuration with respect to the C8 C9 olefinic double bond, as indicated by the C7-C8-C9-C10 torsion angle of À179.96 (15) . The C7 O3 carbonyl group adopts an s-cis configuration with respect to the C8 C9 double bond as indicated by O3-C7-C8-C9 torsion angle of À0.8 (3) . The molecule (excluding H atoms) is nearly planar with a maximum deviation of 0.103 (2) Å at atom O1 of the terminal nitro group. The nitro group is nearly coplanar with the attached C1-C6 benzene ring as indicated by the small dihedral angle of 7.9 (2) . The C1-C6 and C10-C15 benzene rings make a small dihedral angle of 4.27 (8) with each other.

Figure 3
A partial packing diagram of the title compound, showing three separated sheets parallel to (104). The intermolecularinteractions between adjacent sheets are represented as red and blue dashed lines, involving Cg1Á Á ÁCg1 and Cg2Á Á ÁCg2, respectively. Cg1 and Cg2 are the centroids of the C1-C6 and C10-C15 benzene rings, respectively.

Figure 1
The molecular structure of the title compound with atom labels and 30% probability displacement ellipsoids.
represented as blue and red regions on the Hirshfeld surface mapped with electrostatic potential [ Fig. 4(b)]. The electrostatic potential of the F atom is less negative as compared to the O atoms of nitro and carbonyl groups, as indicated by the lighter red region. The HÁ Á ÁO/OÁ Á ÁH contacts are the most populated contacts and contribute 30.2% of the total intermolecular contacts, followed by HÁ Á ÁH (20.6%), HÁ Á ÁC/CÁ Á ÁH (18.0%), HÁ Á ÁF/FÁ Á ÁH (13.1%) and CÁ Á ÁC (10.1%) contacts (Fig. 5). The shortest HÁ Á ÁO/OÁ Á ÁH and HÁ Á ÁF/FÁ Á ÁH contacts are represented as the tips of the pseudo-mirrored sharp spikes and blunt peaks at d e + d i ' 2.3 and 2.4 Å , respectively, which correspond to the C11-H11AÁ Á ÁO3 and C4-H4AÁ Á ÁF1 hydrogen bonds. The characteristic 'wings' are missing in the fingerprint plot of HÁ Á ÁC/CÁ Á ÁH contacts, indicating the absence of any significant C-HÁ Á Á interactions in the crystal. The CÁ Á ÁC contacts, including the intermolecular interactions, appear as a unique 'triangle' focused at d e ' d i ' 1.8 Å . The presence of significantinteractions is supported by the unique pattern of red and blue 'triangles' on the shape-index surface (Fig. 6), and the flat regions on the curvedness surface (Fig. 7) of the benzene rings.

Database survey
The The Hirshfeld surfaces mapped with (a) d norm and (b) electrostatic potential for the central molecule of the title compound surrounded by six neighbouring molecules.

Figure 5
The two-dimensional fingerprint plots of the title compound for different intermolecular contacts and their percentage contributions to the Hirshfeld surface. d i and d e are the distances from the Hirshfeld surface to the nearest atom interior and exterior, respectively, to the surface.
Structural Database (Version 5.39; Groom et al., 2016). The molecular conformations of these two structures are nearly planar, with small dihedral angles of 5.00 (6) and 10.60 (11) , respectively, between the phenyl rings. 6. Synthesis and crystallization 4-Nitroacetophenone (1.65 g, 0.01 mol) and 4-fluorobenzaldehyde (1.24 g, 0.01 mol) were dissolved in methanol (20 ml). A catalytic amount of NaOH was added to the solution dropwise with vigorous stirring. The reaction mixture was stirred for about 6 h at room temperature. The progress of the reaction was monitored by TLC. The formed crude product was filtered, washed repeatedly with distilled water and recrystallized from ethanol to obtain the title chalcone derivative. Yellowish single-crystals suitable for X-ray diffraction were obtained from an acetone solution by slow evaporation at room temperature.

(E)-3-(4-Fluorophenyl)-1-(4-nitrophenyl)prop-2-en-1-one
Crystal data 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.