Crystal structure and Hirshfeld surface analysis of (E)-2-(2,4,6-trimethylbenzylidene)-3,4-dihydronaphthalen-1(2H)-one

In the title compound, C—H⋯O hydrogen bonds and weak C—H⋯π interactions link adjacent molecules into a three-dimensional supramolecular network.


Chemical context
Chalcone (systematic name 1,3-diphenyl-2-propene-1-one) is an aromatic ketone that represents the central core for various derivatives with interesting properties, known as chalcones (Kostanecki & Tambor, 1899). For example, chalcones are found in fruits, vegetables, spices, tea or soy, and find applications as pharmaceuticals (Di Carlo et al., 1999). Chalcones are also major intermediates in the synthesis of natural products and are widely used in synthetic and pharmaceutical chemistry (Dhar, 1981;Ansari et al., 2005) because they have antitumor (Modzelewska et al., 2006), antifungal (Ló pez et al., 2001), anti-inflammatory (Lee et al., 2006), anti-bacterial (Batovska et al., 2009) or antitubercular properties (Lin et al., 2002). In general, chalcones consist of two aromatic rings that are linked by a three-carbon ,-unsaturated carbonyl system, leading to a completely delocalized -electron system. Recently, chalcones have also been used in the field of materials science as non-linear optical devices (Raghavendra et al., 2017). As part of our studies in this area, we report herein the synthesis, crystal structure and Hirshfeld surface analysis of a new chalcone. ISSN 2056-9890

Figure 2
A view along the a axis of the title structure. Blue dashed lines denote the C-HÁ Á ÁO hydrogen bonds which form R 2 2 (20) and R 4 2 (12) ring motifs. C-HÁ Á Á interactions are shown as green dashes lines.
to the C-HÁ Á ÁO interactions described above (Table 1). The overall two-dimensional fingerprint plot is illustrated in Fig. 5a. The Hirshfeld surfaces mapped over d norm are shown for the HÁ Á ÁH, HÁ Á ÁC/ CÁ Á ÁH, HÁ Á ÁO/OÁ Á ÁH, CÁ Á ÁC contacts (McKinnon et al., 2007), and the two-dimensional fingerprint plots are shown in Fig. 5b and 5c, respectively, associated with their relative contributions to the Hirshfeld surface. The largest contribution to the overall crystal packing is from HÁ Á ÁH interactions (66.0%); HÁ Á ÁH contacts are shown in the middle region 1.10 Å < (d i + d e ) < 1.18 Å . HÁ Á ÁC/CÁ Á ÁH contacts contribute 22.3% to the Hirshfeld surface, resulting in two pairs of characteristic wings in the fingerprint plot. The pair of tips appears at 1.10 Å < (d i + d e ) < 1.65 Å . HÁ Á ÁO/ OÁ Á ÁH contacts make a 9.3% contribution to the Hirshfeld surface. The contacts are represented by a pair of sharp spikes in the region 1.05 Å < (d i + d e ) < 1.4 Å in the fingerprint plot. The CÁ Á ÁC contacts are a measure ofstacking interactions and contribute 2.4% to the Hirshfeld surface. They appear as an arrow-shaped distribution at 1.80 Å < (d i + d e ) < 2.0 Å .     The shape-index map of the title molecule (Fig. 3b) was generated in the ranges À1 to 1 Å . The convex blue regions symbolize hydrogen-donor groups and concave red regions symbolize hydrogen-acceptor groups.interactions on the shape-index map are indicated by adjacent red and blue triangles. As can be seen in Fig. 3b, there areinteractions present between adjacent molecules in the title complex.
The curvedness map of the title compound ( Fig. 3c) was generated in the range À4 to 0.4 Å . The large green regions represent a relatively flat (i.e. planar) surface area, while the blue regions demonstrate areas of curvature. The presence of stacking interactions is also evident as flat regions around the rings on the Hirshfeld surface plotted over curvedness.

Synthesis and crystallization
2,4,6-Trimethylbenzylidenetetralone was prepared according to a literature protocol . 10 ml of a NaOH solution (40% wt ) was slowly added to a mixture of tetralone (1 mmol) and 2,4,6-trimethylbenzaldehyde (1 mmol) in ethanol (10 ml) at room temperature and stirred overnight. Then ice-cold water was added to the reaction mixture. The resulting precipitate was filtered off and dried in vacuo. The compound was purified by crystallization from ethanol, resulting in colourless prismatic crystals.

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 2. Hydrogen atoms were fixed geometrically and treated as riding, with C-H = 0.97 Å for methyl groups, 0.96 Å for methylene groups, 0.93 Å for aromatic hydrogen atoms and 0.98 Å for methine groups, with U iso (H) = 1.2U eq (C) or 1.5U eq (C-methyl).

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.