Single crystal X-ray structure analysis for two thiazolylazo indole dyes

To determine the tautomeric form of the hetarylazo indole dye 3-(5-methylthiazol-2-yldiazenyl)-2-phenyl-1H-indole (1), 1-methyl-3-(thiazol-2-yldiazenyl)-2-phenyl-1H-indole (2) was synthesized as a model compound and both molecules were characterized by single crystal X-ray diffraction. (1) crystallized in the monoclinic system, space group C2/c, a = 31.064(2), b = 7.4051(5), c = 27.7138(18) Å, β = 97.617(1)°, V = 6318.9(7) Å3, Z = 8, while dye 2 crystallized in the monoclinic system, space group P21/n, a = 11.4660(11), b = 9.8223(9), c = 14.2049(14) Å, β = 97.418(2)°, V = 1586.4(3) Å3, Z = 4. The asymmetric unit of 1 contains two crystallographically independent molecules, in which geometries and conformations differ slightly, while there is only one molecule in the asymmetric unit for 2. The intermolecular N–H⋯N hydrogen bonds in (1) link the molecules, via parallel, infinite sheets, along the a axis and stabilize the crystal structure; in 2, there is no classical intermolecular hydrogen bond.