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.