N-[2-(4-Chlorophenyl)-5-methyl-4-oxo-1,3-thiazolidin-3-yl]pyridine-3-carboxamide

The title compound, C16H14ClN3O2S, crystallizes with two molecules in the asymmetric unit. In the 1,3-thiazolidine rings, the carbonyl O atoms, the S atoms, the methyl groups and the ring carbon attached to the methyl groups are disordered with occupancy ratios of 0.509 (7):0.491 (7) in one molecule and 0.464 (14):0.536 (14) in the other. The crystal structure is stabilized by intermolecular N—H⋯N, C—H⋯O hydrogen bonds and C—H⋯Cl interactions. In addition, there is a π–π stacking interaction [centroid–centroid distance = 3.794 (3) Å] between the benzene and pyridine rings.

In the 1,3-thiazolidine rings of both the A and B molecules, the carboxyl oxygens, the sulfur atoms, the methyl groups and the ring carbon attached to the methyl groups are disordered with site occupancies of 0.509 (7) and 0.491 (7) for S1, molecule A, and site occupancies of 0.464 (14) and 0.536 (14) for S2, molecule B.
In the 1,3-thiazolidine groups of (I), the dihedral angles between the mean planes of two components of the disordered rings are 10.8 (5)° for molecule A and 15.2 (5)° for molecule B.
The benzene and pyridine rings make dihedral angles of 83.9 (2) and 84.88 (19)° for molecules A and B, respectively.

Refinement
The NH H atoms were found from a difference Fourier map and restrained to 0.86 (2) Å, and refined with U iso (H) = 1.2U eq (N). The C-bound H atoms were geometrically placed (C-H = 0.93-0.98 Å) and refined as riding with U iso (H) = 1.2 or 1.5U eq (C). In the 1,3-thiazolidine groups of the two molecules of (I) in the asymmetric unit, the carboxyl O atoms, the sulfur atoms and the methyl groups and the C atoms of the mentioned ring attached to the methyl groups are disoder with site occupancies of 0.509 (7) and 0.491 (7) for the molecule with S1, and with site occupancies of 0.464 (14) and 0.536 (14) for the molecule with S2. Fig. 1. View of the major components of the two disordered molecules in the asymmetric unit. Displacement ellipsoids for non-H atoms are drawn at the 20% probability level.

Special details
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and tor-

sion angles
Refinement. Refinement on F 2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted Rfactors wR and all goodnesses 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 observed criterion of F 2 > σ(F 2 ) is used only for calculating -R-factor-obs 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.