The crystal structures and Hirshfeld surface analyses of four 3,5-diacetyl-2-methyl-2,3-dihydro-1,3,4-thiadiazol-2-yl derivatives

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 center dot 0.25H(2)O (II), 4-(5-acetamido-3-acetyl-2-methyl-2,3-dihydro-1,3,4-thiadiazol-2-yl)phenyl propionate, C16H19N3O4S (III) and 4-(5-aceta- mido-3-acetyl-2-methyl-2,3-dihydro-1,3,4-thiadiazol-2-yl)phenyl cinnamate chloroform hemisolvate, C22H21N3O4S center dot 0.5CHCl(3) (IV), all crystallize with two independent molecules (A and B) in the asymmetric unit in the triclinic P (1) over bar 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 angstrom). 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)degrees. In the crystals of all four compounds, the A and B molecules are linked via strong N -H center dot center dot center dot O hydrogen bonds and generate centrosymmetric four-membered R-4(4)(28) ring motifs. There are C-H center dot center dot center dot O hydrogen bonds present in the crystals of all four compounds, and in I and II there are also C-H center dot center dot center dot pi interactions present. The intermolecular contacts in the crystals of all four compounds were analysed using Hirshfeld surface analysis and two-dimensional fingerprint plots.