The crystal structure of aceto-acetanilide azo-pigments VI. C.I. Pigment Yellow 4, α-(1-hydroxyethylidene) acetanilide-α-azo-(4′-nitrobenzene)

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Abstract
The crystal structure of C.I. Pigment Yellow 4, α-(1-hydroxyethylidene) acetanilide-α-azo-(4′nitrobenzene), C16H14O4N4, has been determined by single crystal X-ray diffraction techniques. It crystallises in the triclinic system with cell parameters a = 7.691(2) Å, b = 10.247(2) Å, c = 11.195(2) Å, α = 109.00(2)°, β = 73.80(2)°, γ = 112.21(2)°. The space group is P[unk] and there are two molecules per unit cell. The structure was solved by direct methods and least-squares refinement has been completed on three-dimensional data, 2716 reflections (CuKα radiation). The hydrogen atoms have been found and included in the refinement but only those associated with the methyl group have been independently refined. The final residual is 5.4%. The molecule exists as the hydrazone tautomer. It is approximately planar due partly to intramolecular hydrogen bonds and partly due to steric hinderence. The molecules are packed in layers parallel to the ([unk]11) plane with the length parallel to [011] and in columns approximately parallel to a*. Alternate molecules within the columns are in antiparallel. The molecules are linked by van der Waals forces.