Crystal structure of meso-3,3′-(1,4-phenylene)bis(2-phenyl-2,3,5,6-tetrahydro-4H-1,3-thiazin-4-one)

The complete molecule of the title phenylene-bridged bis-heterocycle, a meso compound, is generated by a crystallographic centre of symmetry.

The crystal structure of the title compound -meso-C 26 H 24 N 2 O 2 S 2 with two stereocenters -has half the molecule in the asymmetric unit with the other half generated by a crystallographic center of inversion. The thiazine ring is in a conformation that is between half-chair and envelope [ = 52.51 (17) ]. The phenyl ring on the 2-carbon atom of the thiazine ring is pseudo-axial. The central phenyl ring of the molecule is close to orthogonal to the phenyl rings on either side with an angle of 76.85 (11) between those planes. In the crystal, pairwise, weak C-HÁ Á ÁO hydrogen bonds between the central phenyl ring and the oxygen atoms of neighboring molecules result in continuous strips propagating along the a-axis direction. Hydrophobic interactions of the C-HÁ Á Á type are also observed.

Structural commentary
Compound (I) is highly symmetric with two chiral centers and its meso stereochemistry allows it to straddle the center of inversion in the P2 1 /c space-group (Fig. 1). The thiazine rings adopt a configuration midway between half-chair and envelope [ = 52.51 (17) ], with the sulfur atoms in each forming the back or the flap. On each thiazine ring, the phenyl group on the 2-carbon atom is pseudo-axial. The dihedral angle between the planes of the two substituent phenyl rings is 76.85 (11) . The structure described above shows some similarities and some differences when compared with that of 2,3-diphenyl-2,3,5,6-tetrahydro-4H-1,3-thiazin-4-one, (II) (Yennawar & Silverberg, 2014). In (II), the thiazine ring has an envelope conformation [ = 54.54 (17) ] and the orientation of the phenyl ring on the 3-nitrogen atom about the N-C bond differs by about 90 from the structure of (I), as can be seen in superposition image (Fig. 2).

Figure 3
Packing diagram for (I) showing continuous tape formations linked by weak C-HÁ Á ÁO interactions (dashed lines) propagating along the [100] direction.

Figure 1
The molecular structure of (I) with displacement ellipsoids drawn at the 50% probability level. The asymmetric unit contains half the molecule (unique atoms shown with labels); the unlabeled atoms are generated by the symmetry operation (2 À x, 1 À y, Àz).

Special details
Experimental. The data collection nominally covered a full sphere of reciprocal space by a combination of 4 sets of ω scans each set at different φ and/or 2θ angles and each scan (10 s exposure) covering -0.300° degrees in ω. The crystal to detector distance was 5.82 cm. SADABS V2.05 (BRUKER, 2001) was used for absorption correction. R(int) was 0.0303 before and 0.0175 after correction. The Ratio of minimum to maximum transmission is 0.8572. The λ/2 correction factor is 0.0015. 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. 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 > 2sigma(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. 0.0334 (9) 0.0291 (10) 0.0329 (9) 0.0018 (7) 0.0064 (7) 0.0013 (7)  C12 0.0323 (9) 0.0405 (11) 0.0310 (9) 0.0029 (8) −0.0002 (7) 0.0019 (8)  C13 0.0294 (8) 0.0371 (11) 0.0371 (10) −0.0014 (7) 0.0031 (7) −0.0012 (8)  N1 0.0342 (8) 0.0359 (9) 0.0373 (8) 0.0054 (7) 0.0085 (6) 0.0083 (7)