Pigment Yellow 213, a commercial azo pigment used for car coatings, exists in a greenish-yellow alpha-phase, and a brown beta-phase. The X-ray powder diagram of the alpha-phase could be indexed in multiple ways, and it was not possible to determine which is the correct one, even by means of LeBail fits with GSAS. Therefore the lattice parameters of the triclinic unit cell were determined by electron diffraction. Lattice energy minimisations were used to predict possible crystal structures, but attempts for subsequent Rietveld refinements were ambiguous. For all calculated structures, electron diffraction patterns were simulated and compared with the experimental electron diffraction intensities, but the correct structure could not be found, since the molecule adopts an unusual conformation which was never observed before, and which was not regarded in the lattice energy minimisations. Finally the crystal structure was solved from laboratory X-ray powder data using real-space methods with TOPAS. A subsequent Rietveld refinement (TOPAS) on synchrotron data converged with a smooth difference curve (Rp = 2.38%, Rwp = 3.12%, chi2 = 1.34). For the first time, pair distribution analyses (PDF) were applied to organic pigments. The PDF analysis of the alpha-phase, based on synchrotron powder data, confirmed the determined crystal structure. The beta-phase is a nanocrystalline powder which does not show any reliable Bragg-peak in the X-ray diffractogram. The PDF analysis of the beta-phase reveal that (1) the beta-phase exhibits a layer structure with a layer distance of about 3.3Å like the alpha-phase, (2) the local structures of the beta-phase is similar to that of the alpha-phase, and (3) the correlation length (i.e. domain size) of the beta-phase is below 5 nm. Thus the PDF method is able extract some information on the crystal structure of this organic compound from the X-ray powder diagram, although the crystallite size is so low and the powder diagram consists of some humps only. In the talk the corresponding methods (Electron diffraction, lattice energy minimisation, and pair distribution function analysis) will be briefly explained.

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