Polymorph prediction of organic pigments

The crystal structure of several industrially important organic pigments namely C.I. Pigment Violet 23, C.I. Pigment Red 202 and C.I. Pigment Yellow 139 were predicted using the Cerius2 Polymorph Predictor in combination with XRPD patterns. After generation and energy minimisation of the candidate structures for each pigment, their calculated powder patterns were compared with those obtained experimentally using X-ray diffraction. The structures which best fitted the experimental powder patterns were regarded as possible structures of the compound; finally, a rigid body Rietveld refinement was performed to validate the choice of the structure. The structure of C.I. Pigment Violet 23 has not previously been published while the predicted structures of C.I. Pigment Red 202 and C.I. Pigment Yellow 139 were in accordance with the published structures. The work demonstrates that pigment crystal structure can be predicted using a low quality X-ray powder diffraction pattern.