Crystal structure, Hirshfeld surface analysis and DFT study of (2Z)-2-(2,4-dichlorobenzylidene)-4-[2-(2-oxo-1,3-oxazolidin-3-yl)ethyl]-3,4-dihydro-2H- 1,4-benzothiazin-3-one

The title compound, C20H16Cl2N2O3S, is built up from a dihydrobenzothiazine moiety linked by -CH- and -C2H4- units to 2,4-dichlorophenyl and 2-oxo-1,3-oxazolidine substituents, where the oxazole ring and the heterocyclic portion of the dihydrobenzothiazine unit adopt envelope and flattened-boat conformations, respectively. The 2-carbon link to the oxazole ring is nearly perpendicular to the mean plane of the dihydrobenzothiazine unit. In the crystal, the molecules form stacks extending along the normal to (104) with the aromatic rings from neighbouring stacks intercalating to form an overall layer structure. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H⋯H (28.4%), H⋯Cl/Cl⋯H (19.3%), H⋯O/O⋯H (17.0%), H⋯C/C⋯H (14.5%) and C⋯C (8.2%) interactions. Weak hydrogen-bonding and van der Waals interactions are the dominant interactions in the crystal packing. Density functional theory (DFT) optimized structures at the B3LYP/ 6-311G(d,p) level are compared with the experimentally determined molecular structure in the solid state. The HOMO - LUMO behaviour was elucidated to determine the energy gap.