Crystal structures of two (Z)-2-(4-oxo-1,3-thiazolidin-2-ylidene)acetamides

The crystal structures of two (oxothiazolidin-2-ylidene)acetamides, namely (Z)-2-[2-(morpholin-4-yl)-2-oxoethylidene]thiazolidin-4-one and (Z)-N-(4-methoxyphenyl)-2-(4-oxothiazolidin-2-ylidene)acetamide are described and compared with a related structure.


Structural commentary
The molecular structures of the title compounds, (I) and (II), are illustrated in Figs. 1 and 2, respectively. Both compounds crystallize in the monoclinic space group P2 1 /c. The Z conformation about the C8 C9 bond is observed for both compounds and favours SÁ Á ÁO contacts of 2.6902 (18) and 2.738 (3) Å in (I) and (II), respectively. The morpholine ring in compound (I) adopts a chair conformation. The twist angle between the thiazolidine (S1/N2/C9-C11) and amide mean planes (O1/N1/C7/C8) is 10.71 (10) in (I) and 2.36 (14) in (II). In (II), the benzene ring plane is inclined to the mean plane of the thiazolidine ring by 20.60 (12) . The bond lengths ISSN 2056-9890 and angles in both compounds are similar to those observed for compound (III), mentioned above.

Supramolecular features
In the crystal of (I), molecules are linked by N-HÁ Á ÁO hydrogen bonds forming C(6) chains running parallel to the a-axis direction (Table 1 and Fig. 3). The dihedral angle between thiazolidine mean planes is 6.12 (7) . There are three non-classical C2-H2AÁ Á ÁS1 i , C5-H5BÁ Á ÁO3 ii and C6-H6BÁ Á ÁO3 iii (Table 1)  In crystal of (II), both amide moieties participate in the formation of N-HÁ Á ÁO hydrogen bonds (see Table 2). These two types of N-HÁ Á ÁO hydrogen bonds give rise to the formation of two independent C(8) and C(6) chains, running parallel to the b-and c-axes, respectively (see Figs. 4 and 5). Here, the dihedral angle between the thiazolidine mean planes in the N1-H1Á Á ÁO3 i and N2-H2Á Á ÁO2 ii motifs is 79.21 (16) . The combination of these chain motifs generates a twodimensional network lying parallel to the bc plane. Each molecule acts as both a double donor and a double acceptor of N-HÁ Á ÁO hydrogen bonds. The molecules of (II) are linked into aggregated R 4 4 (28) tetramers, which serve as the building blocks of the layers (see Fig. 6). The molecular structure of title compound (I), with the atom labelling. Displacement ellipsoids at the 50% probability level.

Figure 4
View of the N1-H1Á Á ÁO3 i C(8) chain motif along the b-axis of compound (II cooled to room temperature and diluted with a 0.5 N HCl solution (5 ml). The precipitates formed of the 1,3-thiazolidinones, were filtered off. The crude products were additionally purified by refluxing a suspension of the thiazolidine in MeCN, followed by hot filtration. Colourless crystals of compounds (I) and (II) were obtained by slow evaporation of the respective compound in a solution of DMSO.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. For both compounds, the hydrogen atoms were included in calculated positions and refined using the riding model: C-H = 0.93-0.97 Å with U iso (H) = 1.5U eq (C-methyl) and 1.2U eq (C) for other C-bound H atoms. The NH H atoms were located in difference-Fourier maps and freely refined. Reaction scheme for the title compounds.

Special details
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.

(Z)-N-(4-Methoxyphenyl)-2-(4-oxothiazolidin-2-ylidene)acetamide (II)
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.22 e Å −3 Δρ min = −0.33 e Å −3 Special details 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.