Crystal structure prediction of organic pigments

Abstract

The present work investigates the feasibility of predicting crystal structures of industrially important pigments when only low quality XRPD patterns are available. Despite the commercial significance of organic pigments only few crystal structures of these materials have been reported. Pigments are practically insoluble in most solvents and, therefore, it is difficult to grow a single crystal of good enough quality for the structure determination. In industry, pigments are produced by precipitation reactions leading to very fine powders. The crystallites are often so small that they cause a considerable line broadening in X-ray powder diffraction. Therefore, a powder pattern of limited quality is usually the only information available. The structures of organic pigments PV19, PV23 and PR202 were successfully predicted using the Polymorph Predictor of Cerius in combination with XRPD patterns of limited quality. After generation and energyminimization of the possible structures, their powder patterns were compared to the experimental ones. On this basis, structures of pigments were chosen from the list of all the structures. Rietveld refinement was used to validate the right choice of the structures. m29.o04