Crystal structure of 3-(benzo[d]thiazol-2-yl)-6-methyl-2H-chromen-2-one

The title molecule is almost planar, with an intramolecular S⋯O=C contact. The packing is a layer structure with dimeric units connected by a C—H⋯O=C hydrogen bond.


Chemical context
Benzothiazole and its derivatives are important heterocyclic aromatic compounds. Benzothiazole can be readily substituted at the C-2 position of the thiazole ring . Compounds containing a benzothiazolyl group have found numerous applications in medicine and in nonlinear optics (Sigmundová et al., 2007). Benzothiazole derivatives can also display strong fluorescence and luminescence in the solid state and in solution (Wang et al., 2010). Benzothiazole compounds as incorporated in organic light-emitting diodes have attracted substantial attention because of their notable photovoltaic properties (Ghanavatkar et al., 2020). Recently, we have synthesized novel heterocyclic derivatives involving the benzothiazole moiety, many of which showed significant biological and fluorescence activities Khedr et al., 2022).
Coumarin is a natural product with the systematic name 2Hchromen-2-one. Its derivatives represent an important class of organic heterocycles. Thus, they are constituents of many intensively investigated and commercially important organic fluorescent materials; they also display important biological activities and are found in synthetic drugs (Curini et al., 2006). Furthermore, many coumarin compounds are current photosensitizers with valuable applications in medicinal chemistry (Bansal et al., 2013). Because of their photochemical properties, coumarin compounds have found applications in nonlinear optical materials, solar energy collectors and charge-transfer agents (Kim et al., 2011), and also as daylight fluorescent pigments, tunable dye lasers, fluorescent probes and components of organic light-emitting diodes (Christie & Lui, 2000). The emission intensities of coumarin chromo-phores depend on the nature of their substituents at various sites (Ż amojć et al., 2014).
In two recent papers (Abdallah et al., 2022(Abdallah et al., , 2023, we have given a more extensive list of references concerning the properties of benzothiazoles and coumarins, including many of our own publications in these fields. Some decades ago, we reported the syntheses and characterizations of novel coumarin derivatives that have found applications as laser dyes (Elgemeie, 1989); these included 3-(benzo[d]thiazol-2-yl)-2H-chromen-2-one, the desmethyl analogue of title compound 4, a benzothiazole-based coumarin derivative which was synthesized by the reaction of 2-(cyanomethyl)benzothiazole with salicyaldehyde. Afterwards, other research groups utilized essentially the same reaction to synthesize different derivatives of the same heterocyclic framework, including compound 4 (Chao et al., 2010;Makowska et al., 2019).

Structural commentary
The structure of compound 4 is shown in Fig. 2. Its bond lengths and angles may be regarded as normal; a selection is presented in Table 1. The chromene and benzothiazole ring systems are planar as expected, with respective r.m.s. deviations of 0.020 and 0.015 Å ; the angle between these planes is only 3.01 (3) , so that the whole molecule almost planar. A short intramolecular S11Á Á ÁO2 contact of 2.792 (1) Å is observed. The desmethyl analogue (Abdallah et al., 2022) has, as expected, a closely similar molecular structure, with an SÁ Á ÁO C contact of 2.727 (2) Å and an interplanar angle of 6.47 (6) , but is not isotypic to 4.

Database survey
The searches employed the routine ConQuest (Bruno et al., 2002), part of Version 2022.3.0 of the Cambridge Structural Database (Groom et al., 2016). A search for structures containing both a coumarin and a benzothiazole ring system in the same residue gave 16 hits. After excluding ring systems with more extended annelation and molecules where the ring systems were not directly bonded to each other, 7 hits remained. In all of these, the benzothiazole was bonded via its 2-position. The structure with refcode AKUCUG (Bakthadoss & Selvakumar, 2016)

Refinement
The title crystal was a non-merohedral two-component twin. The orientations are related by a 180 rotation around the reciprocal axis c*. The structure was refined using the HKLF5 method, whereby the relative volume of the smaller twin component refined to 0.387 (1). For non-merohedral twins thus refined, R int is not a valid concept, and the number of reflections should be interpreted with caution, because the equivalent reflections in the intensity file have already been merged.
Crystal data, data collection and structure refinement details are summarized in Table 3. The methyl group was included as an idealized rigid group allowed to rotate but not tip (C-H = 0.98 Å and H-C-H = 109.5 ). Other H atoms were included using a riding model starting from calculated positions (aromatic C-H = 0.95 Å ). The U iso (H) values were fixed at 1.5 times U eq of the parent C atoms for methyl groups and at 1.2 times U eq for the other H atoms.  Computer programs: CrysAlis PRO (Rigaku OD, 2022), SHELXT (Sheldrick, 2015a), SHELXL2018 (Sheldrick, 2015b) and XP (Siemens, 1994).

Figure 3
Packing diagram of compound 4, viewed perpendicular to (211). Dashed lines indicate 'weak' hydrogen bonds. Atom labels indicate the asymmetric unit. H atoms other than H17 have been omitted.

3-(Benzo[d]thiazol-2-yl)-6-methyl-2H-chromen-2-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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )