Crystal structure and Hirshfeld surface analysis of 4-{[(E)-4-(heptyloxy)benzylidene]amino}-N-(naphthalen-2-yl)-1,3-thiazol-2-amine

Charge-assisted C—H⋯π hydrogen bonds along with π–π interactions stabilize the crystalline state. Intermolecular interactions are quantified by Hirshfeld surface analysis.


Chemical context
Schiff bases, i.e. compounds containing the azomethine group (-CH N-or >C N-), are important because of their physiological and pharmacological properties. They are typically synthesized by the condensation of primary amines and active carbonyl groups. The pharmacological activities of Schiff bases include anti-bacterial, anti-fungal, anti-cancer and anti-viral properties (Wang et al., 2001;Yadav & Singh, 2001).
One of the most important scaffolds in drug design and heterocyclic chemistry is thiazole, which is widely found in various pharmacologically active substances and in some naturally occurring compounds (Ayati et al., 2015). Various thiazole-bearing compounds have shown activities such as anti-bacterial, anti-fungal, anti-inflammatory, anti-hypertensive, anti-HIV, anti-tumor, anti-filarial, anti-convulsant, herbicidal, insecticidal, schistosomicidal and anthelmintic (Bharti et al., 2010). The synthesis of thiazole derivatives by various methods and their biological evaluation have been described by several researchers and the thiazole nucleus has therefore attracted a lot of interest for the development of pharmacologically active compounds (Breslow, 1958). In our studies, a new Schiff base, 4-{[(E)-4-(heptyloxy)benzylidene]amino}-N-(naphthalen-2-yl)-1,3-thiazol-2-amine, was obtained in crystalline form from the reaction of 2-amino-4-(2- ISSN 2056-9890 naphthyl)thiazole with 4-N-(heptyloxy)benzaldehyde. We report here the synthesis and the crystal and molecular structures of the title compound, including a Hirshfeld surface analysis to assess the relative importance of the various intermolecular interactions on the crystal packing.

Figure 2
A view of the crystal packing of the title compound. The C-HÁ Á Á(ring) interactions are indicated by dashed lines.
Cg3 is the centroid of the C5-C10 ring.

Figure 3
The Hirshfeld surfaces of the title compound mapped over (a) d norm , and (b) electrostatic potential.

Synthesis and crystallization
The title compound was prepared by adding 4-N-(heptyloxy)benzaldehyde (0.1947 g, 0.885 mmol) dropwise to a constantly stirring solution of 2-amino-4-(2-naphthyl)thiazole (0.2 g, 0.885 mmol) in 1-propanol (10 ml). The reaction was catalysed by NaOH (0.1 g) and was stirred for 3 h in a water bath at 278-283 K. The reaction was monitored with thin-layer chromatography (TLC) using a 3:7 ratio of ethyl acetate to nhexane (R f = 0.775). The precipitate was filtered, washed with 1-propanol, and dried. The resulting solid was further purified by recrystallization from ethanol and diethyl ether. Single crystals of the title compound suitable for X-ray analysis were obtained by slow evaporation of an acetone solution (yield 81.7%, m.p. 387.5-389.5 K).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The C-bound H atoms were placed in idealized positions and refined using a riding model: C-H = 0.93-0.97 Å with U iso (H) = 1.5U eq (C-methyl) and 1.2U eq (C) for other C-bound H atoms. Two-dimensional fingerprint plots, showing the relative contribution of the atom-pair interactions to the Hirshfeld surface.    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.