Abstract
The crystal and molecular structure of C. I. Pigment Red 3, 4-methyl-2-nitrophenylazo-2-naphthol has been determined by x-ray diffraction techniques. It crystallises in the monoclinic system with cell parameters a = 16.316 ± 0.038 Å, b = 12.860 ± 0.033 Å, c = 6.960 ± 0.018 Å, β = 102.00 ± 0.05°. The space group is P21/a 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, 1601 reflections (CuKα radiation). The hydrogen atoms have been found and included but not refined. The final residual is 7.8%. The molecule exists as the hydrazone tautomer and intramolecular hydrogen bonds keep the molecules approximately planar; the slight deviations from planarity are explained by packing considerations. The molecules are packed in columns with alternate molecules antiparallel and are linked by van der Waals forces.