3-Chloro-4-[2-(4-chlorobenzylidene)hydrazinylidene]-1-methyl-3,4-dihydro-1H-2λ6,1-benzothiazine-2,2-dione

In the title compound, C16H13Cl2N3O2S, the dihedral angle between the aromatic rings is 6.62 (2)° and the C=N—N=C torsion angle is 176.2 (4)°. The thiazine ring shows an envelope conformation, with the S atom displaced by 0.633 (6) Å from the mean plane of the other five atoms (r.m.s. deviation = 0.037 Å). The Cl atom is an an axial conformation and is displaced by 2.015 (6) Å from the thiazine ring plane. In the crystal, molecules are linked by C—H⋯O interactions, generating a three-dimensional network. Very weak aromatic π–π stacking interactions [centroid–centroid separations = 3.928 (2) Å] are also observed.

In the title compound, C 16 H 13 Cl 2 N 3 O 2 S, the dihedral angle between the aromatic rings is 6.62 (2) and the C N-N C torsion angle is 176.2 (4) . The thiazine ring shows an envelope conformation, with the S atom displaced by 0.633 (6) Å from the mean plane of the other five atoms (r.m.s. deviation = 0.037 Å ). The Cl atom is an an axial conformation and is displaced by 2.015 (6) Å from the thiazine ring plane. In the crystal, molecules are linked by C-HÁ Á ÁO interactions, generating a three-dimensional network. Very weak aromaticstacking interactions [centroid-centroid separations = 3.928 (2) Å ] are also observed.   Table 1 Hydrogen-bond geometry (Å , ).  Benzothiazine derivatives are versatile chiral ligands (Harmata et al., 2006) and show various biological activities (Ahmad et al., 2010a, Misu & Togo, 2003. As part of our ongoing studies in this area (Shafiq et al., 2011a,b), we now describe the synthesis and structure of the title compound, (I) (Fig. 1).

Related literature
The dihedral angle between the aromatic rings C1-C6 and C11-C16 is 6.6 (2)° and the C9=N2-N3=C10 torsion angle is 176.2 (4)°. The conformation of the C1/C6/C8/C9/N1/S1 thiazine ring is an envelope, with the S atom displaced by -0.633 (6) Å from the mean plane of the other five atoms (r.m.s. deviation = 0.037 Å). This displacement is smaller than that seen in related structures (Shafiq et al., 2013). In (I), atom C7 is displaced from the mean plane of the ring by 0.541 (7) Å and Cl1, in an axial site, is displaced by 2.015 (6) Å. Atom C8 is a stereogenic centre with an S configuration in the arbitrarily-chosen asymmetric unit. Nevertheless, crystal symmetry indicates a racemic mixture.
In the crystal, moelcules are linked by C-H···O interactions (Table 1) to generate a three-dimensional network (Fig. 2).
Chlorination of the Schiff base was undertaken using N-chloro succinimide and dibenzoylperoxide (Shafiq et al., 2011b).
The crude product was re-crystallized from ethyl acetate and dichloromethane solution (1:1 v/v) to obtain yellow blocks of the title compound.

Refinement
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.

Figure 2
Partial packing diagram of (I), showing H···O interactions as double-dashed lines and π-π stacking as open pink lines. 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.