The crystal structure of C.I. Pigment Red 6, 4-chloro-2-nitrophenylazo-2-naphthol

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Abstract
The crystal and molecular structure of C.I. Pigment Red 6, 4-chloro-2-nitrophenylazo-2-naphthol has been determined by x-ray diffraction techniques. It crystallizes in the monoclinic system with cell parameters a = 12.293 ± 0.005 Å, b = 6.958 ± 0.003 Å, c = 15.780 ± 0.005 Å, β = 94.22 ± 0.10° The space group is P21/c and there are four molecules per unit cell. The structure was solved using direct methods and least-squares refinement has been completed on three-dimensional data with θ less than 55° (CuKα radiation) The hydrogen atoms have been found and included but not refined The molecule exists as the hydrazone tautomer and intramolecular hydrogen bonds keep the molecules approximately planar; the slight deviations from planarity are, in the main, explained by packing considerations. The molecules are packed in columns with alternate molecules antiparallel and are linked by van der Waals forces.