XRD crystallographic analysis

The ozonide of 2,3-diphenyl-2-bomene can be prepared by photosensitized addition of oxygen to the corresponding epoxide (313), as shown in equation 103. The structure of product 314 was determined by single-crystal XRD crystallographic analysis. It should be pointed out that both 302 and 314 have Oe envelope conformation for the 1,2,4-trioxolane... 

Ciyoscopic determination of the molecular weight of f-Bu2Mg in benzene solution pointed to a dimer (86), the structure of which was conhrmed by H and C NMR spectroscopy and ultimately determined by XRD crystallographic analysis . ... 

Apphcation of XRD crystallographic methods for structural analysis of organic compounds is today quite a routine, though non-trivial, undertaking. However, given the high... 

The metastable y-form crystal structure prior to the slow phase transitions was determined by the X-ray crystallographic analysis, but the crystal structures of three other new polymorphs ( -, r)- and e-forms) were undetermined by the same X-ray analysis, because these polymorphs were obtained as powder samples. Since the nearly racemic e-form crystals could be obtained as the monophasic powder sample by just leaving the crystallization mixture untouched, its crystal structure was solved from its X-ray diffraction (XRD) data by the direct-space approach using the Monte Carlo algorithm with the subsequent Rietveld refinement.26,27 Consequently, the Rwp value has been satisfactorily converged to 9.1%. 

Structure of [5]-heIiphos obtained by XRD. The structures of the pyroelectric 4,8,12-trioxa-12c-phospha-4,8,12,12c-tetrahydrodibenzo[cd,mn]pyrene (61), of oligo(thioarylene)cyclophosphonites 62, of the Diels-Alder cyclo-adducts 63, 64, and of a rotational isomer of a l,2-diphenyl-3,4-diphosphinidene-cyclobutene (65) have been determined by X-ray crystallographic analysis. 

Powder X-Ray Diffraction (XRD) In order to investigate into the crystalline modification of the generated API crystals and their solid dispersions, crystallographic analysis was carried out by means of powder diffraction. These measurements were carried out with a Phillips wide and small angle X-ray diffractometer under nitrogen gas atmosphere. The XRD measurements of the powder samples were repeated after a certain time in order to ensure that the generated polymorphic form of PCM is stable. 

Because x-rays are particularly penetrating, they are very usefiil in probing solids, but are not as well suited for the analysis of surfaces. X-ray diffraction (XRD) methods are nevertheless used routinely in the characterization of powders and of supported catalysts to extract infomration about the degree of crystallinity and the nature and crystallographic phases of oxides, nitrides and carbides [, ]. Particle size and dispersion data are often acquired with XRD as well. 

As illustrated by Eig. 4.13, an electron microscope offers additional possibilities for analyzing the sample. Diffraction patterns (spots from a single-crystal particle and rings from a collection of randomly oriented particles) enable one to identify crystallographic phases as in XRD. Emitted X-rays are characteristic for an element and allow for a determination of the chemical composition of a selected part of the sample. This technique is referred to as energy-dispersive X-ray analysis (EDX). 

Analogous to the DuP 747 study, complete crystallographic information was not possible on the fosinopril sodium polymorphic system [25], Two known polymorphs (A and B) were studied via a multidisciplinary approach (XRD, IR, NMR, and thermal analysis). Complementary spectral data from IR and solid state 13C NMR revealed that the environment of the acetal sidechain of fosinopril sodium differed in the two forms. In addition, possible cis-trans isomerization about the CgN peptide bond may exist. These conformational differences are postulated as the origin of the observed polymorphism in fosinopril sodium in the absence of the crystallographic data for form B (single crystals not available). 

The examples illustrate the strong points of XRD for catalyst studies XRD identifies crystallographic phases, if desired under in situ conditions, and can be used to monitor the kinetics of solid state reactions such as reduction, oxidation, sulfidation, carburization or nitridation that are used in the activation of catalysts. In addition, careful analysis of diffraction line shapes or - more common but less accurate-simple determination of the line broadening gives information on particle size. 

Certain considerations made for structural analysis of compounds containing OOH groups mentioned in previous sections apply here too however, the characterization is usually more difficult and requires concurrent evidence from various techniques to ascertain the presence of the C—OO—C moiety. The main characterization tools are NMR, looking for the effects of —OO—on the resonance of nearby atoms and XRD for compounds with single crystals of good crystallographic quahty. 

In addition, structural similarities can often be determined from careful interpretation of XRD powder patterns. The powder patterns of offretite and erionite look quite different, but are easily understood in terms of the crystallographic consequences of a change in the ordered layer stacking sequence (11), cf. Figure 4. In offretite, the layers are stacked in an AAB sequence, while in erionite, they are ordered in an AABAAC arrangement that doubles one of the crystallographic unit cell parameters. The doubled c-parameter is readily deduced from an analysis of the XRD powder pattern of erionite. Another framework structure effect, isomorphous substitution, can result in changing unit cell sizes, observed as shifts in XRD line positions for such systems as X and... 

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