Crystal structure, Hirshfeld surface analysis and inter­action energy and DFT studies of 3-{(2Z)-2-[(2,4-di­chloro­phen­yl)methyl­idene]-3-oxo-3,4-di­hydro-2H-1,4-benzo­thia­zin-4-yl}propane­nitrile

The title compound, C(18)H(12)Cl(2)N(2)OS, consists of a di­hydro­benzo­thia­zine unit linked by a –CH group to a 2,4-di­chloro­phenyl substituent, and to a propane­nitrile unit is folded along the S⋯N axis and adopts a flattened-boat conformation. The propane­nitrile moiety is nearly perpendicular to the mean plane of the di­hydro­benzo­thia­zine unit. In the crystal, C—H(Bnz)⋯N(Prpnit) and C—H(Prpnit)⋯O(Thz) (Bnz = benzene, Prpnit = propane­nitrile and Thz = thia­zine) hydrogen bonds link the mol­ecules into inversion dimers, enclosing R (2) (2)(16) and R (2) (2)(12) ring motifs, which are linked into stepped ribbons extending along [110]. The ribbons are linked in pairs by complementary C=O⋯Cl inter­actions. π–π contacts between the benzene and phenyl rings, [centroid–centroid distance = 3.974 (1) Å] may further stabilize the structure. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H⋯H (23.4%), H⋯Cl/Cl⋯H (19.5%), H⋯C/C⋯H (13.5%), H⋯N/N⋯H (13.3%), C⋯C (10.4%) and H⋯O/O⋯H (5.1%) inter­actions. Hydrogen bonding and van der Waals inter­actions are the dominant inter­actions in the crystal packing. Computational chemistry calculations indicate that the two independent C—H(Bnz)⋯N(Prpnit) and C—H(Prpnit)⋯O(Thz) hydrogen bonds in the crystal impart about the same energy (ca 43 kJ mol(−1)). Density functional theory (DFT) optimized structures at the B3LYP/6–311 G(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.