1-Ethyl-4-{2-[1-(4-methylphenyl)ethylidene]hydrazinylidene}-3,4-dihydro-1H-2λ6,1-benzothiazine-2,2-dione

In the title compound, C19H21N3O2S, the dihedral angle between the aromatic rings is 6.7 (2)° and the C=N—N=C torsion angle is 178.0 (2)°. The conformation of the thiazine ring is an envelope, with the S atom displaced by 0.802 (2) Å from the mean plane of the other five atoms (r.m.s. deviation = 0.022 Å). In the crystal, molecules are linked by C—H⋯O interactions, generating C(5) chains propagating in [010]. A weak C—H⋯π interaction is also observed.

In the title compound, C 19 H 21 N 3 O 2 S, the dihedral angle between the aromatic rings is 6.7 (2) and the C N-N C torsion angle is 178.0 (2) . The conformation of the thiazine ring is an envelope, with the S atom displaced by 0.802 (2) Å from the mean plane of the other five atoms (r.m.s. deviation = 0.022 Å ). In the crystal, molecules are linked by C-HÁ Á ÁO interactions, generating C(5) chains propagating in [010]. A weak C-HÁ Á Á interaction is also observed.   Table 1 Hydrogen-bond geometry (Å , ).
MS acknowledges the HEC Pakistan for providing a PhD fellowship and the University of Sargodha for the X-ray diffraction facility. The dihedral angle between the C1-C6 and C13-C18 aromatic rings is 6.68 (15)° and the C10=N2-N3=C11 torsion angle is 177.98 (19)°. The conformation of the C1/C6/C9/C10/N1/S1 thiazine ring is an envelope, with the S atom displaced by 0.802 (2) Å from the mean plane of the other five atoms (r.m.s. deviation = 0.022 Å). A very similar conformation was observed in a related structure (Shafiq et al., 2013). Atoms C7 and C8 in (I) are displaced from the mean plane of the thiazine ring by -0.416 (5) and 0.704 (6) Å, respectively.
In the crystal, the moelcules are linked by C-H···O interactions (Table 1) to generate C(5) chains propagating in the b axis direction. A weak C-H···π interaction to the C13-C18 ring also occurs (Table 1).

Refinement
The H atoms were placed in calculated positions (C-H = 0.93-0.97 Å) and refined as riding. The methyl group was allowed to rotate, but not to tip, to best fit the electron density. The constraint U iso (H) = 1.2U eq (C) or 1.5U eq (methyl C) was applied.  The molecular structure of (I), showing displacement ellipsoids at the 50% probability level. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.45 e Å −3 Δρ min = −0.40 e Å −3

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.