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Electron diffraction, X-ray powder diffraction, lattice energy minimisation, and pair distribution function analysis to determine the crystal structures of Pigment Yellow 213, C23H21O9N5

Martin U. Schmidt 1Stephan Brühne 1Anette Rech 1Juergen Bruening 1Edith Alig 1Lothar Fink 1Christian Buchsbaum 1Alexandra Wolf 1Jürgen Glinnemann 1Jacco Van de Streek 1Fabia Gozzo 2Michela Brunelli 3Frank Stowasser 4Tatiana Gorelik 5Ute Kolb 5

1. Institut für Anorganische und Analytische Chemie, Johann Wolfgang Goethe-Universität, Max-von-Laue-Strasse 7, Frankfurt am Main 60438, Germany
2. Swiss Light Source, Paul Scherrer Institute, Villigen PSI 5232, Switzerland
3. Europen Synchrotron Radiation Facility (ESRF), 6, Jules Horowitz, Grenoble 38000, France
4. Novartis Pharma AG, Basel 4002, Switzerland
5. Johannes Gutenberg Universität, Institut für Physikalische Chemie, Jakob Welder Weg, 11, Mainz 55128, Germany


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.brueEPDIC.gif


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Related papers

Presentation: Oral at 11th European Powder Diffraction Conference, Microsymposium 8, by Martin U. Schmidt
See On-line Journal of 11th European Powder Diffraction Conference

Submitted: 2008-04-30 19:50
Revised:   2009-06-07 00:48