X-Ray crystal structure analysis and determination of azo-enamine and hydrazone-imine tautomers of two hetarylazo indole dyes

Two hetarylazo indole dyes were analyzed by single crystal X-ray diffraction. Dye 1 , C₁₈H₁₄N₄O, crystallises in the monoclinic system, space group P2₁/c, with two independent molecules in the asymmetric unit. Dye 2 , C₂₀H₁₆N₄, also crystallises in the monoclinic system, space group P2₁/n, Z  = 4. In both compounds, there are two intramolecular C–H...N hydrogen bonds which influenced the molecular conformation between the azo group and the indole ring system and its phenyl substituent. Each of the independent molecules of dye 1 interact through the N–H...N hydrogen bond, whereas no classical intermolecular hydrogen bond was observed in dye 2 . The molecules of dye 1 and dye 2 are packed differently in both structures.