The crystal structures of two (oxothiazolidin-2-ylidene)acetamides, namely (Z)-2-[2-(morpholin-4-yl)-2-oxoethylidene]thiazolidin-4-one, C9H12N2O3S, (I), and (Z)-N-(4-methoxyphenyl)-2-(4-oxothiazolidin-2-ylidene)acetamide, C12H12N2O3S, (II), are described and compared with a related structure. The Z conformation was observed for both the compounds. In (I), the morpholin-4-yl ring has a chair conformation and its mean plane is inclined to the thiazolidine ring mean plane by 37.12 (12)°. In (II), the benzene ring is inclined to the mean plane of the thiazolidine ring by 20.34 (14)°. In the crystal of (I), molecules are linked by N—H...O hydrogen bonds, forming C(6) chains along the b-axis direction. The edge-to-edge arrangement of the molecules results in short C—H...O and C—H...S interactions, which consolidate the chain into a ribbon-like structure. In the crystal of (II), two N—H...O hydrogen bonds result in the formation of C(8) chains along the b-axis direction and C(6) chains along the c-axis direction. The combination of these interactions leads to the formation of layers parallel to the bc plane, enclosing R44(28) rings involving four molecules
