The crystal structure of aceto-acetanilide azo-pigments VII. A polymorph (α) of C.I. Pigment Yellow 5, α-(1-hydroxyethylidene) acetanilide-α-azo-(2′-nitrobenzene)

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Abstract
The crystal structure of a polymorph (α) of C.I. Pigment Yellow 5, α-(1-hydroxyethylidene) acetanilide-α-azo-(2′-nitrobenzene), C16H14O4-N4, has been determined by single crystal X-ray diffraction techniques. It crystallises in the monoclinic system with cell parameters a = 7.593 ∓ 0.001 Å, b = 20.029 ∓ 0.004 Å, c = 10.217 ∓ 0.002 Å, β = 101.87 ∓ 0.02°. The space group is P21/n and there are four molecules per unit cell. The structure was solved from the coordinates of Hansa Yellow 5G and least-squares refinement has been completed on three-dimensional data, 2547 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 6.6%. The molecule exists as the hydrazone tautomer and intramolecular hydrogen bonds keep the molecule approximately planar. The molecules are packed in layers approximately parallel to the ([unk]01) plane and in columns parallel to the a axis. Alternate molecules within the columns are in antiparallel. The molecules are linked by van der Waals forces. It is concluded that the present structure is isomorphous with Hansa Yellow 5G and C.I. Pigment Yellow 1.