Powder x-ray data

Much success in determining crystal structures has been achieved through high-quality powder X-ray data of polycrystalline powders [57], Structures which have been elucidated include P(EO), LiCF, SO, P(E0)3NaC104, P(EO)4KSCN, P(EO)4 RbSCN, P(EO)4 NH4SCN, and P(EO)3LiN(SO,CF3)2[18,58], All crys-... 

It is difficult to prepare stretched oriented fibres and such fibres may differ in their polymer chain conformation compared with the unstretched materials. Furthermore the quality of the single crystal X-ray data is poor and difficult to interpret. In contrast power X-ray data of relatively high quality may be obtained from polycrystalline polymer films. Lightfoot, Mehta and Bruce (1992) have obtained the first crystal structure of a polymer-salt complex, PEOjiNaClQ from powder X-ray data. Fig. 5.11(h). The structure is similar to the corresponding PEOjiNal structure, the PEO chains are wrapped around the Na ions with each Na ... 

In mid 1951 two young scientists joined the laboratory staff, Drs. T. B. Reed, a crystallographer, and D. W. Breck, an inorganic chemist. Reed had hoped to work with me on molecular sieves. In the applicant interview, I had challenged him to determine the detailed structures of the A and X zeolites from powder x-ray data, pore size and volume information, and ion exchange properties. He was assigned, however, to a different project in another group. 

These were remarkable accomplishments considering the size of the unit cells and the complexity of the structures. I remember posing the problem to Dr. Linus Pauling when he visited our laboraory in the mid fifties. Some 25 years earlier he had published on the structure of the zeolite natrolite and several feldspathoids [22]. He assured me that it was a waste of time to even try to determine the detailed structure of zeolites from powder x-ray data. 

In August 1952 Breck located the powder x-ray data for mineral faujasite and realized that it was very similar to that of the X zeolite. We obtained about 50 mg. of faujasite and studied it carefully. The x-ray pattern was indeed very similar to that of X. The adsorption capacity was somewhat lower but similar. The silica/alumina ratio was 4.7 compared to 2.5 for X. The cations in faujasite were calcium, magnesium, and barium, not sodium as in X. It was clear that X and faujasite were isostructural but with different compositions. Further similarities and differences could not be studied at that time due to the limited supply of faujasite. 

Carbide s patent department had reservations because in their experience, composition of matter claims had to be drawn very narrowly to be valid and as such were frequently easy to circumvent. We convinced them that the unique properties that make A and X useful are singular results of their specific chemical composition and the arrangement of atoms in the crystal lattice of the zeolites. To our knowledge, the use of powder x-ray data as a finger print to uniquely identify a specific crystal structure was a new concept in patent protection. 

Powder X-Ray Data. We believe that S1 NMR provides a more accurate determination of framework composition than elemental analysis since the measurement Is essentially Independent of any Impurities that may be occluded In the zeolite pores. Therefore, we used the values of Sl/Al derived from the NMR data to follow the variation of unit-cell size with composition. 

The preparation and characterization of CD-PNA has been described in some detail previously. All analytical data (CHN, NMR, IR, Raman) support the assignment as a 1 1 incluson complex, but it has to date defied attempts to prepare crystals adequate for x-ray determination. Powder x-ray data indicate that it is not a simple admixture of the two ingredients, and ultraviolet spectroscopy shows that a strong 1 1 complex can exist in solution (Benesi-Hildebrand analysis), and that the complex is oriented such that the nitro group entered the CD cavity first (circular dichroism and NMR). 

Figure 2 Partial Raman (top) and MAS NMR spectra (bottom) from hydrate samples recovered from Cascadia, taken at lOK and 173K, respectively. The spectral signatures indicate that methane is the principal guest for both large (major peak) and small cages(minor peaks). The line intensities show that the popidations are in an approximate 3-4 1 ratio (for large small cages), confirming the powder X-ray data assignment that it is a si hydrate. mbsf= meters below sea floor, cm bsf cm below sea floor. From ref. 41...

Single crystal X-ray data (Enraf Nonius) Powder X-ray data (Rigaku D-Max III VC)... 

Methods for the preparation of the selenate Bi2(Se04)3 have been investigated and the compound has been characterized. Powder X-ray data have been collected for the pyrochlore Bi2Ru207, Bi2U06, and 811982703. ... 

Recently Krogmann et al postulated a cation-deflcient, partially oxidized formulation for this material, K o.5lr(CO)2Cl2, and a columnar structure in the solid (16). This one-dimensional structure is consistent with the observed diamagnetism, stoichiometry, IR spectra, dc conductivity, and visual appearance of the complexes. Preliminary powder x-ray data support this formulation with a short 2.86 A Ir-Ir distance. This information sets a basis for the interpretation of detailed optical, electrical, and magnetic measurements that will help in further understanding of the chemistry and physics of one-dimensional inorganic complexes. 

These comparatively low concentrations are no doubt responsible in part for the lack of detailed molecular structures in the literature. Coupled with this is the fact that complex mixtures are invariably isolated in the first parts of most procedures the number of isolated single species is rare indeed. Chromatographic results, volatility studies and powder X-ray data all pointed at an early date to the presence of groups of isomers in isolate fractions rather than the presence of unique compounds. Finally, the application of mass spectroscopy to the study of petroporphyrins clearly established that this was the case, revolving about classic studies involving material isolated... 

Powder X-ray data were reported for I3AICI4 and I5AICI2, but not indexed ). 

No single crystal X-ray data have been reported yet for this group of compounds. However, some powder X-ray data are known. 

Recent work has suggested a trace of bromide (arising from impurities in the starting materials) to be associated with a cation-deficient species (310), that is, Ki.78Pt(CN)4Bro.o34(H20)2. Further work is necessary to establish the relationship between Ki.74Pt(CN)4(H20)i.8 and K1.78 Pt(CN)4Bro.o34(H20)2 especially since recent powder x-ray data indicate that these complexes are not equivalent (310). 

Krogmann et al. (516) have also reported the preparation of the isoelectron-ic mixed valent Ir2(C0)4Cl2(02CCH3) species from a mixture of hexachloro-iridate(IV) and formic and acetic acids. Preliminary powder x-ray data indicate that the dinuclear species possess extremely short Ir-Ir spacings of 2.78 A and a helical superstructure of 0.7 A in diameter. Further work is necessary to clarify the physical and chemical properties of these Ir - complexes in solution and the solid state. 

Figure 16 shows one projection of the lattice structure of zeolite ZSM-12. The structure is approximately that originally reported (32) although a recent refinement of S3nichrotron powder X-ray data by Gies and co-workers (33) establishes the unit cell symmetry as 2/z ... 

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