The crystal structure of C.I. Pigment Red 2, 1′-(2,5-dichlorophenyl)azo-2′hydroxy-3′-phenylamidonaphthalene

Abstract

Abstract The crystal and molecular structure of C.I. Pigment Red 2, l′-(2,5-dichlorophenyl)azo-2′-hydroxy-3′-phenylamidonaphthalene has been determined by x-ray diffraction techniques. It crystallizes in the monoclinic system with cell parameters a = 10.309 ± 0.006 Å, b = 9.051 ± 0.003 Å c = 21.991 ± 0.015 Å, β = 104.33 ± 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 35° (CnKα radiation). The hydrogen atoms have been found and included but not refined. The final residual is 15.3%. The molecule is probably in the form of the hydrazone tautomer. The intramolecular hydrogen bonds keep most of the molecule approximately planar while it appears that the remainder is held in the same plane due to steric hinderence between the molecules. The molecules are packed in columns with alternate molecules antiparallel and are linked by van der Waals forces.