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Same Crystal (same + crystal)
Selected AbstractsA comparison of a microfocus X-ray source and a conventional sealed tube for crystal structure determinationJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2009Thomas Schulz Experiments are described in which a direct comparison was made between a conventional 2,kW water-cooled sealed-tube X-ray source and a 30,W air-cooled microfocus source with focusing multilayer optics, using the same goniometer, detector, radiation (Mo,K,), crystals and software. The beam characteristics of the two sources were analyzed and the quality of the resulting data sets compared. The Incoatec Microfocus Source (IµS) gave a narrow approximately Gaussian-shaped primary beam profile, whereas the Bruker AXS sealed-tube source, equipped with a graphite monochromator and a monocapillary collimator, had a broader beam with an approximate intensity plateau. Both sources were mounted on the same Bruker D8 goniometer with a SMART APEX II CCD detector and Bruker Kryoflex low-temperature device. Switching between sources simply required changing the software zero setting of the 2, circle and could be performed in a few minutes, so it was possible to use the same crystal for both sources without changing its temperature or orientation. A representative cross section of compounds (organic, organometallic and salt) with and without heavy atoms was investigated. For each compound, two data sets, one from a small and one from a large crystal, were collected using each source. In another experiment, the data quality was compared for crystals of the same compound that had been chosen so that they had dimensions similar to the width of the beam. The data were processed and the structures refined using standard Bruker and SHELX software. The experiments show that the IµS gives superior data for small crystals whereas the diffracted intensities were comparable for the large crystals. Appropriate scaling is particularly important for the IµS data. [source] Apparent shortening of the Csp3,Csp3 bond analysed via a variable-temperature X-ray diffraction study in racemic 1,1,-binaphthalene-2,2,-diyl diethyl bis(carbonate)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2009Susanta K. Nayak Crystal structure determination at room temperature [292,(2),K] of racemic 1,1,-binaphthalene-2,2,-diyl diethyl bis(carbonate), C26H22O6, showed that one of the terminal carbon,carbon bond lengths is very short [Csp3,Csp3 = 1.327,(6),Å]. The reason for such a short bond length has been analysed by collecting data sets on the same crystal at 393, 150 and 90,K. The values of the corrected bond lengths clearly suggest that the shortening is mainly due to positional disorder at two sites, with minor perturbations arising as a result of thermal vibrations. The positional disorder has been resolved in the analysis of the 90,K data following the changes in the unit-cell parameters for the data sets at 150 and 90,K, which appear to be an artifact of a near centre of symmetry relationship between the two independent molecules in the space group P at these temperatures. Indeed, the unit cell at low temperature (150 and 90,K) is a supercell of the room-temperature unit cell. [source] Chiral ureas with two electronegative substituents at 1-N: An unusual case of coexisting pyramidal and almost planar 1-N atoms in the same crystal,CHIRALITY, Issue 7 2009Oleg V. Shishkin Abstract XRD studies of structure of N -acetoxy- N -methoxyurea and N,N -bis(methoxycarbonyl)- N -methoxyimide have revealed that in N -methoxy- N -X-ureas (X = OAc, Cl, OMe, N+C5H5) the additional shortening of NOMe bond took place, which arising from an nO(Me) -,*NX anomeric orbital interaction. XRD studies of N -chloro- N -ethoxyurea crystal have revealed the presence of two kinds of anomeric nitrogen configuration in the ONCl group in the form of a pyramidal configuration and a planar configuration for same 1-N nitrogen atom. XRD studies of N -4-chlorobenzoyloxy- N -ethoxyurea have revealed that the degree of pyramidality of the 1-N nitrogen in N -aroyloxy- N -alkoxyureas is tuned by orientation of benzoyl group with respect to the NO bond, which in turn depends of size of N -alkoxy group. Chirality, 2009. © 2008 Wiley-Liss, Inc. [source] Application of High Spatial Resolution Laser Ablation ICP-MS to Crystal-Melt Trace Element Partition Coefficient DeterminationGEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 1 2007Maurizio Petrelli ICP-MS; ablation laser; éléments en trace; figure de mérite; coefficients de partage entre cristal et liquide In this contribution we evaluate the capabilities of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) using a 12 ,m spot size. Precision, accuracy and detection limits were assessed on the USGS BCR-2G reference material. We demonstrate that the 12 ,m LA-ICP-MS analyses of experimentally-grown amphibole and garnet are in excellent agreement with secondary ion mass spectrometry (SIMS) trace element determinations on the same crystals. The 12 ,m spot size configuration was subsequently used to determine trace element crystal-melt partition coefficients (Dc/m) for a wide range of trace elements in amphibole in equilibrium with a basanitic melt. The following strategy to determine accurately and evaluate Dc/m is proposed. One or more major elements determined previously by electron probe microanalysis (EPMA) was used to ensure consistency between EPMA and the composition of the aerosol produced by the laser ablation. Measured Dc/m values were successively evaluated using the lattice strain model. The use of this strategy significantly improved the precision and accuracy of Dc/m determination when a LA-ICP-MS configuration with a high spatial resolution was employed. Dans cet article nous évaluons les potentialités de l'ablation laser couplée à un spectromètre de masse à plasma induit (LA-ICP-MS) en travaillant avec un diamètre d'impact de 12 ,m. Précision, justesse et limites de détections sont évaluées sur le matériau de référence BCR-2G de l'USGS. Nous démontrons que les analyses LA-ICP-MS faites avec un diamètre de 12 ,m sur les amphiboles et des grenats synthétiques sont en excellent accord avec les déterminations d'éléments en trace effectuées sur les mêmes cristaux par sonde ionique (SIMS). Ce diamètre d'impact de 12 ,m a donc été sélectionné pour déterminer les coefficients de partage cristal/liquide (Dc/m) pour un grand nombre d'éléments en trace dans une amphibole en équilibre avec un liquide basanitique. Nous proposons la stratégie d'analyse suivante, qui assure une détermination exacte des coefficients de partage Dc/m. Un ou plusieurs des éléments majeurs déterminés auparavant par microsonde électronique (EMPA) est utilisé pour garantir la consistance des données entre EMPA et la composition de l'aérosol produit par l'ablation laser. Les Dc/m mesurés sont ensuite évalués en utilisant le modèle de contrainte de réseau. L'utilisation de cette stratégie améliore de manière significative la précision et la justesse des déterminations de Dc/m quand elle est couplée à l'utilisation d'un système LA-ICP-MS de grande résolution spatiale. [source] | ||||||||||