Crystal structure and Hirshfeld surface analysis and energy frameworks of 1-(2,4-dimethylphenyl)-4-(4-methoxyphenyl)naphthalene

In the title naphthalene derivative, the mean plane of the naphthalene ring system makes dihedral angles of 65.24 (12)° with the dimethylphenyl ring and 55.82 (12)° with methoxyphenyl ring. The latter two rings are inclined to each other by 59.28 (14)°.


Chemical context
Naphthalene and its derivatives are known for their wide range of applications in the field of pharmaceuticals. They are also used in the manufacturing of colorants, surface-active agents, resins, disinfectants and insecticides. These derivatives play a vital role in the control of microbial infection (Rokade & Sayyed, 2009) and in the chemical defence against biological enemies (Wright et al., 2000). Compounds with a naphthalene moiety have been shown to exhibit significant anti-TB activity (Upadhayaya et al., 2010).

Structural commentary
The molecular structure of the title compound is illustrated in Fig. 1. The benzene ring (C9-C14) of the naphthalene moiety is substituted by a dimethylphenyl ring (C2-C4/C6-C8) and a methoxyphenyl ring (C19-C24) para to each other. The naphthalene ring system is slightly bent with the two aryl rings being inclined to each other by 3.06 (15) . Its mean plane makes dihedral angles of 65.24 (12) with the dimethylphenyl ring (C2-C4/C6-C8) and 55.82 (12) with methoxyphenyl ring (C19-C24). The latter two rings are inclined to each other by ISSN 2056-9890 59.28 (14) . The methoxy group (C22/O1/C25) lies out of the plane of the benzene ring (C19-C24) to which it is attached by 11.3 (3) . The bond lengths and bond angles are similar to those reported for 1,4-diphenylnaphthalene, which crystallized with two independent molecules in the asymmetric unit (Lima et al., 2012).

Supramolecular features
In the crystal, there is only one significant intermolecular interaction present, viz. a C-HÁ Á Á interaction linking adjacent molecules to form chains propagating along the a-axis direction (Table 1 and Fig. 2).

Analysis of the Hirshfeld surfaces, interaction energies and energy frameworks
The Hirshfeld surfaces and two-dimensional fingerprint plots were generated in order to explore and quantify the weak intermolecular interactions using the program CrystalExplorer 17.5 (Turner et al., 2017). The electrostatic potentials were calculated using TONTO, integrated in the program Crystal-Explorer (Spackman et al., 2008;Jayatilaka et al., 2005). The Hirshfeld surfaces of the title compound were mapped over d norm , electrostatic potential, curvedness and shape index ( Fig. 3a-3d); depending upon the closeness to the adjacent molecules, the colour patches are mapped differently on the Hirshfeld surface (Fig. 3e). Two-dimensional fingerprint plots showing the result of all intermolecular contacts (McKinnon et al., 2007) are presented in Fig. 4a; d i (x axis) and d e (y axis) are the closest internal and external distance from a given point on the Hirshfeld surface. The fingerprint plot of HÁ Á ÁH contacts, which represent the largest contribution to the Hirshfeld surface (64.6%), are shown as a distinct pattern with a minimum value of d e = d i ' 1.2 Å (Fig. 4b). The CÁ Á ÁH/ HÁ Á ÁC interactions appear as the next largest region of the fingerprint plot, highly concentrated at the edges, having almost the same d e + d i ' 2.7 Å (Fig. 4c), with on overall contribution of 27.1%. The OÁ Á ÁH/HÁ Á ÁO interactions on the fingerprint plot, which contribute 5.2% of the total Hirshfeld surfaces, with d e + d i ' 2.8 Å (Fig. 4d) are shown as two symmetrical wings. The CÁ Á ÁC contacts, which are the measure ofstacking interactions, occupy 3.1% of the Hirshfeld surfaces and appear as a unique triangle at about d e = d i ' 1.8 Å (Fig. 4e). These weak interactions mostly contribute to the packing of the title compound.
The interaction energies between the molecules are obtained using monomer wavefunctions at the B3LYP/6- The molecular structure of the title compound, with the atom labelling. Displacement ellipsoids are drawn at 50% probability level. Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
The crystal packing of the title compound, viewed along the b axis. The C-HÁ Á Á interactions (see Table 1) are shown as dashed lines, and only the H atom H25C (grey ball) has been included.
31G(p,d) level. The total interaction energy, which is the sum of scaled components, was calculated for a 3.8 Å radius cluster of molecules around the selected molecule (Fig. 5a). The scale factors used in the CE-B3LYP benchmarked energy model (Mackenzie et al., 2017) are given in Table 2. The energies calculated by the energy model reveals that the dispersion energy contributes significantly to the interactions in the crystal ( Table 3). The energy framework calculations were performed for a cluster of molecules present in 2 Â 2 Â 2 unit cells using the CE-B3LYP energy model. Energies between molecular pairs are represented as cylinders joining the centroids of pairs of molecules with the cylinder radius proportional to the magnitude of the interaction energy. Energy frameworks were constructed for E elec as red cylinders, E dis as green and E tot as blue ( Fig. 5b-5d) and these cylinders represent the relative strength of molecular packing in different directions. Thus the supramolecular architecture of the crystal structure is visualized uniquely by energy frameworks.

Synthesis and crystallization
A reaction scheme for the synthesis of the title compound is illustrated in Fig. 6. To a solution of m-xylyl-p-anisyl tethered benzo[c]furan (0.16 g, 0.49 mmol) in dry xylenes (15 ml   the crude adduct was dissolved in dry CH 2 Cl 2 (15 ml) and then kept at 273 K. To this, triflic acid (0.02 g, 0.13 mmol) was added and the mixture stirred at room temperature for 10 min. After completion of the reaction (monitored by TLC), it was poured into ice-water (20 ml) and then extracted with CH 2 Cl 2 (2 Â 10 ml). The organic layers were combined and washed with aq. NaHCO 3 (2 Â 10 ml) and then dried (Na 2 SO 4 ). Removal of the solvent followed by column chromatographic purification (silica gel, 5% ethyl acetate in hexane) afforded the title compound as a yellow solid (0.20 g, 79%). Yellow block-like crystals of the title compound, suitable for X-ray diffraction analysis, were obtained by slow evaporation of a solution in CHCl 3 (m.p. 351-353 K).

Refinement
Crystal data collection and structure refinement details are summarized in Table 4. All H atoms were positioned geometrically and refined using a riding model: C-H = 0.93-0.96 Å with U iso (H) = 1.5 U eq (C-methyl) and 1.2U eq (C) for other H atoms.

1-(2,4-Dimethylphenyl)-4-(4-methoxyphenyl)naphthalene
where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.27 e Å −3 Δρ min = −0.19 e Å −3 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.