Structures in Mo-Ru-Si system by powder and anomal X-ray diffraction

Abstract

anlog) were solved from laboratory diffractometer data. The results can be useful for the development of more potent and selective A2aAR antagonists which are important for the treatment of Morbus Parkinson. Complexity of the investigated compounds solved by global optimization technique [2] ranges from 22 to 46 atoms in an asymmetric unit. Powder diffraction data were recorded both using Bragg-Brentano and DSH geometry (to reduce texture). It was astonishing that in the case of very strong texture one can encounter problems even in the indexing procedure. In such cases crystal structure solution process from powder data verifies the indexing and space group determination results.[1] Muller C.E., Sauer R., Geis U., Frobenius W., Talik P., Paw owski M., Arch. Pharm. Pharm. Med. Chem., 1997, 330, 181-189 The preliminary step to solve crystal structure is the determination of the space group. In case of powder diffraction data the peak overlap makes difficult the recognition of systematically absent reflections and therefore the extinction symbol identification. We have developed a new approach [1] based on the statistical analysis of the normalized intensities extracted by Le Bail method from the diffraction pattern. In order to improve the results new algorithms have been carried out regarding: a) the removal of impurity peaks; b) the background level determination; c) the variance associated to integrated intensity estimated; d) the selection of reflections relevant for the extinction group recognition; e) the graphic interface improvement The new approach has been implemented in EXPO2005, the evolution of EXPO2004 [2], and has been successfully tested using a large set of experimental data.[1] Altomare A., Caliandro R., Camalli M., Cuocci C., da Silva I., Giacovazzo C., Moliterni A.G.G., Spagna R., J. Appl . The phases and are isotypes of the FeSi and FeCr structures respectively. The structures of the and phases were determined ab-initio from synchrotron X-ray powder diffraction (XRPD) data. All of these phases are partially disorder with statistical occupancy of sites by the various metallic atoms. In order to increase the contrast between Mo and Ru and to obtain a crystallographic composition, X-Ray powder patterns were performed at the Mo-K threshold (20 keV) so as to use the anomal effect. Therefore, multi refinement pattern using two wave lengths (one near the Mo Threshold, the other out) has been performed. Subsequently, an assessment of the site occupancy rates allowed to specify the distribution of the Mo (Z = 42) and Ru (Z = 44) atoms. Extension of the stability domain of phase Mo 4+x Ru 9-x Si 5 (0 x 1) is understood on the basis of the XRPD results and electronic properties calculation (KKR method) as a function of the composition [1].[1] Littner A., François M., Tobola J., Elkaim E., Malaman B., Vilasi M., Intermetallics, 2005, in The methodology has been extended a little further and some new algorithms will be presented to simplify the procedure in a unique improved step. Using an approach der...