Vacuum sublimation and crystallography of quinacridones

Quinacridones are pigments of outstanding light, heat and chemical fastness. Single crystals of linear unsubstituted quinacridone and 4,11-dichloroquinacridone were grown by the vacuum sublimation method at about 425°C and 390°C respectively under a vacuum of 0.3 torr. The sublimation products are always γ-form quinacridone and β-form 4,11-dichloroquinacridone no matter what respective polymorphic forms are used as the starting material. Exothermic effects at transition temperatures were observed for both materials on heating by TGA and DSC techniques. The space groups and unit-cell dimensions were determined by the precession method. The powder patterns are indexed by single-crystal data. The size, shape, and orientation of the molecules as well as the general structure features are discussed.