| Summary: | The title compounds, 4-(5-acetamido-3-acetyl-2-methyl-2,3-dihydro-1,3,4-thiadiazol-2-yl)phenyl benzoate, C20H19N3O4S (I), 4-(5-acetamido-3-acetyl-2-methyl-2,3-dihydro-1,3,4-thiadiazol-2-yl)phenyl isobutyrate 0.25-hydrate, C17H21N3O4S·0.25H2O (II), 4-(5-acetamido-3-acetyl-2-methyl-2,3-dihydro-1,3,4-thiadiazol-2-yl)phenyl propionate, C16H19N3O4S (III) and 4-(5-acetamido-3-acetyl-2-methyl-2,3-dihydro-1,3,4-thiadiazol-2-yl)phenyl cinnamate chloroform hemisolvate, C22H21N3O4S·0.5CHCl3 (IV), all crystallize with two independent molecules (A and B) in the asymmetric unit in the triclinic P\overline{1} space group. Compound II crystallizes as a quaterhydrate, while compound IV crystallizes as a chloroform hemisolvate. In compounds I, II, III (molecules A and B) and IV (molecule A) the five-membered thiadiazole ring adopts an envelope conformation, with the tetrasubstituted C atom as the flap. In molecule B of IV this ring is flat (r.m.s. deviation 0.044 Å). The central benzene ring is in general almost normal to the mean plane of the thiadiazole ring in each molecule, with dihedral angles ranging from 75.8 (1) to 85.5 (2)°. In the crystals of all four compounds, the A and B molecules are linked via strong N—H...O hydrogen bonds and generate centrosymmetric four-membered R44(28) ring motifs. There are C—H...O hydrogen bonds present in the crystals of all four compounds, and in I and II there are also C—H...π interactions present. The intermolecular contacts in the crystals of all four compounds were analysed using Hirshfeld surface analysis and two-dimensional fingerprint plots.
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