Crystal structure and Hirshfeld surface analysis of (E)-N-(4-propyloxybenzylidene)benzo[d]thiazol-2-amine

In the crystal, the molecules are linked by C—H⋯N and weak C—H⋯π hydrogen bonds and very weak π–π stacking interactions. Two-dimensional fingerprint plots show that the largest contributions to the crystal stability come from H⋯H and C⋯H/H⋯C interactions.

The title compound, C 17 H 16 N 2 OS, was synthesized by a condensation reaction between 2-amino benzothiazole and 4-N-propoxybenzaldehyde. The benzo[d]thiazole ring system is nearly planar (r.m.s. deviation 0.0088 Å ) and makes a dihedral angle of 3.804 (12) with the phenyl ring. The configuration about the C N double bond is E. In the crystal structure, pairs of C-HÁ Á ÁN hydrogen bonds and C-HÁ Á Á interactions link the molecules into inversion dimers with an R 2 2 (16) ring motif. These dimers are additionally linked by weak stacking interactions between the phenyl rings, leading to a layered arrangement parallel to (010). Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the packing arrangement are from HÁ Á ÁH (47.9%) and CÁ Á ÁH/HÁ Á ÁC (25.6%) interactions.

Chemical context
Benzothiazole is one of the most important heterocyclic compounds, comprising of a sulfur and a nitrogen atom that constitute the core structure of thiazole. Benzothiazole is a weak base, and is widely found in bioorganic and medicinal chemistry with application in drug discovery as a pharmacologically and biologically active compound (Quin & Tyrell, 2010). Benzothiazole and its derivatives show numerous biological activities such as antimicrobial, anticancer, anthelmintic or anti-diabetic. They have also found application in industry as antioxidants and vulcanization accelerators (Achaiah et al., 2016).
Schiff bases (Schiff, 1864) are nitrogen analogues of aldehydes or ketones in which the corresponding functional group has been replaced by an imine or azomethine group. They can be synthesized from the reaction of primary amines with an aldehyde or a ketone under particular conditions. Schiff bases are some of the most widely used organic compounds, utilized, for example, as catalysts, pigments and dyes, intermediates in organic synthesis, or as polymer stabilizers. Moreover, Schiff bases exhibit a broad range of biological activities such as antiviral, antibacterial, anti-inflammatory, antimalarial, anti- ISSN 2056-9890 fungal, anti-proliferative and antipyretic properties (Bhoi et al., 2015).
In the context given above, we report here the synthesis, molecular and crystal structure of the Schiff base C 17 H 16 N 2 OS, comprising a benzothiazole moiety.

Structural commentary
The asymmetric unit of the title compound is comprised of one molecule ( Fig. 1 (Sen et al., 2018;Kansiz et al., 2018), which are in the range of 1.262 (3)-1.270 (3) Å . The methyl group of the propyl chain is moved out by 59.2 (3) from the mean plane of the rest of the molecule.

Hirshfeld surface analysis
Hirshfeld surface analysis together with two-dimensional fingerprint plots are a powerful tool for the visualization and interpretation of intermolecular contacts in molecular crystals (Spackman & Jayatilaka, 2009). The corresponding surfaces and fingerprint plots were obtained using CrystalExplorer (Turner et al., 2017). The d norm and molecular electrostatic potential maps for the title compound are shown in Fig Table 1 Hydrogen-bond geometry (Å , ).
Cg2 is the centroid of the C1-C6 phenyl ring.

Figure 2
A view of the crystal packing of the title compound. Intermolecular interactions are displayed by dotted lines. The symmetry code refers to Table 1.

Figure 3
The Hirshfeld surface of the title compound mapped over (a) d norm and (b) electrostatic potential, showing the C-HÁ Á ÁN hydrogen bond.

Figure 1
The molecular structure of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 40% probability level.
3b, respectively, with the prominent hydrogen-bonding interactions shown as red spots. The red spots identified in Fig. 3a correspond to the HÁ Á ÁN contacts resulting from hydrogen bond C-HÁ Á ÁN (

Synthesis and crystallization
2-Amino benzothiazole (0.3 g, 2 mmol) was dissolved in 10 ml of 1-propanol in a 50 ml borosilicate glass beaker. 4-N-Propoxybenzaldehyde (0.328 g, 2 mmol) was then added dropwise into the mixture under stirring, in the presence of a catalytic amount of glacial acetic acid. The reaction mixture was then placed inside an unmodified household microwave oven and was irradiated for 32 min (eight pulses each of 4 min) at 540 W power, with short interruptions of one minute. The progress of the reaction was monitored by thin-layer chromatography using ethyl acetate and n-hexane (3:7 v:v) as eluent (R f = 0.69). The formed precipitate was filtered off, washed with 1-propanol, and dried. The resulting solid was further purified by recrystallization from n-hexane to give the pure imine as a crystalline solid (yield: 72.4%, m.p. 357-358 K).

sup-2
Acta Cryst. (2020). E76, 1591-1594 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.