Different patterns of supramolecular assembly in constitutionally similar 6-arylimidazo[2,1-b][1,3,4]thiadiazoles

Four imidazo[2,1-b][1,3,4]thia­diazo­les containing a simply-substituted 6-aryl group have been synthesized by reaction of 2-amino-1,3,4-thia­diazo­les with bromo­acetyl­arenes using micro­wave irradiation and brief reaction times. 6-(2-Chloro­phen­yl)imidazo[2,1-b][1,3,4]thia­diazole, C₁₀H₆ClN₃S, (I), 6-(2-chloro­phen­yl)-2-methyl­imidazo[2,1-b][1,3,4]thia­diazole, C₁₁H₈ClN₃S, (II), 6-(3,4-di­chloro­phen­yl)imidazo[2,1-b][1,3,4]thia­diazole, C₁₀H₅Cl₂N₃S, (III), and 6-(4-fluoro-3-meth­oxy­phen­yl)-2-methyl­imidazo[2,1-b][1,3,4]thia­diazole, C₁₂H₁₀FN₃OS, (IV), crystallize with Z' values of 2, 1, 1 and 2 res­pec­tively. The mol­ecular skeletons are all nearly planar and the dihedral angles between the imidazole and aryl rings are 1.51 (8) and 7.28 (8)° in (I), 9.65 (7)° in (II), 10.44 (8)° in (III), and 1.05 (8) and 7.21 (8)° in (IV). The mol­ecules in (I) are linked by three independent C-H...N hydrogen bonds to form ribbons containing alternating R₂²(8) and R₄⁴(18) rings, and these ribbons are linked into a three-dimensional array by three independent π-stacking inter­actions. Both (II) and (III) contain centrosymmetric dimers formed by π-stacking inter­actions but hydrogen bonds are absent, and the mol­ecules of (IV) are linked into centrosymmetric R₂²(8) dimers by C-H...N hydrogen bonds. Comparisons are made with a number of related compounds.