Ciystal structures

Fig. 4. Model of the ciystal structure of zeolites X, Y, and the mineral faujasite. At the tight is shown the tetrahedral arrangement of tmncated octahedra surrounding one large cavity. On the left the packing model of zeohte X is shown, containing three types of Na cations.

Despite the relatively short history of the chemistry of fluoride compounds, several thousands of binary and ternary fluoride compounds have been described, and their systematization is well developed [39 - 41]. Significant progress was achieved in the study of the crystal chemistry of fluoride compounds thanks to the ionic character of their chemical bonds and corresponding simplicity of their ciystal structure. The structure of these kinds of compounds is defined primarily by the geometry and the energy of mainly... 

M3Ta02F4 and M3Nb02p4, where M = K, Rb, Cs, form ciystal structures similar to that of Rb3TiF6, which is described by Bode and Voss [189]. The structure of the compounds can be described as a tetragonally distorted cubic cell of the (NFL )3FeF6 type, the structure of which is described by Steward and Rockby [190]. 

All ciystal structures were determined in the laboratory of Prof. A. L. Rheingold. We thank Drs. D. Beach and M. Camey of Chevron Chemical Co. for helpful discussions. 

The packing arrangement of atoms or molecules in a crystalline solid phase is generally not unique, and for organic molecules in particular, it is common for two or more crystalline forms of the same substance to exist. The most familiar example in elemental terms is Graphite and Diamond. Both are composed entirely of the element Carbon, however their ciystal structures are very different, and so too are their physical properties. Calcium Carbonate is another common example with three polymorphic forms Calcite, Aragonite and Vaterite. 

Fig. 7.2. Ciystal structures of ubiquitin ligases discussed in this chapter. The structures are colored as following The HECT N lobe is purple, C lobe green, and the E2 blue, the c-Cbl TKB domain is green, the linker yellow, RING domain purple, the phosphopeptide orange.

Fig. 16. Ciystal structure of human HO-1 (163). The heme and His25 ligand are shown. The proximal and distal helices are highlighted. Note the break iu the normal helical pattern in the distal helix directly over the heme.

Figure 8. A framework representation of the X-ray ciystal structure of 10-PhCH2NH3SCN.

The ciystal structure of dipicolinic acid was first solved by Takusagawa et... 

The two gold thiophenedithiolenes give ciystal structures with very similar structural features. The average Au-S bond lengths exhibited are 2.327 A for 8 and 2.303 A for lOc, " consistent with previous An dithiolenes. As with the Ni complexes, no significant intermolecular short contacts are... 

A single ciystal structure has been reported only for form A, which was crystallized from ethanol [9]. The space group was P2i2i2i, and contained 4 molecules in the unit cell. The unit cell parameters were reported as a= 8.677(5), i=9.311(8), and c=9.727(4), with 1 molecule in the asymmetric unit. The molecule has a bent chain conformation with one carbon out of the plane of the other five carbon atoms, which are coplanar. The molecules stack with their chain axes approximately parallel. 

Fig. 13. Ciystal structure of 2-tert-butyl-4-(4 -methoxyphenyl)-5.6-dihydronaptho [1.2-b]- -phosphorin ii " ...

The most common measurements of pigment properties comprise elemental analysis, impurity content, ciystal structure, particle size and shape, particle size distribution, density, and surface area. These parameters are measured so that pigments producers can better contiol production, and set up meaningful physical and chemical pigments specifications. Measurements of these properties are not specific only to pigments. The techniques applied are commonly used to characterize powders and solid materials, and the measuring methods have been standardized in various industries. 

Heating a deoxygenated sample of crystalline 2 at 180 °C for 10 min afforded 48% each of the fullerene 1 and the antipodal bisadduct 3 (96% conversion no other components detected). The bisadduct 3 was isolated and its structure confirmed by NMR spectroscopy and FAB mass spectrometry, as well as by single ciystal structure analysis. 

The small octaazacryptand, 2, is selective for fluoride [44], with extremely high affinity, log Ka = 10-11 in aqueous solution [44-46], As anticipated, the ciystal structure of 2 with fluoride showed the halide to be encapsulated Figure 5) [44], Later theoretical and modeling studies indicated that the small size of the cavity could preclude encapsulation of larger anions [45],... 

If there is one molecule/unit cell, (I) the molecule may racemize if the cavity size is greater than 11.5 A, resulting in some disorder in the ciystal structure. If there are two molecules/unit cell, (II) one molecule may invert and one may stay the same, (III) both molecules may racemize but equilibrium conditions lead to one molecule reverting and one inverting, (IV) both molecules racemize, but to different extents, or (V) both molecules racemize equally. 

Dr. D.W. Breck was the discoverer of the Y zeolite, a co-discoverer of the unique catalytic cracking activity of the X zeolite, and with Dr. T.B. Reed worked out the ciystal structures of A and X. He was certainly one of the world s outstanding zeolite scientists. 

LESBURG, C. A., ZHAI, G. Z., CANE, D. E., CHRISTIANSON, D. W., Ciystal structure of pentalenene synthase Mechanistic insights on terpenoid cyclization reactions in biology, Science, 1997,277,1820-1824. 

See, also, I. Hargittai, Ciystal Structures and Culture In Memoriam Khudu Mamedov (1927-1988). Struct. Chem. 2007, 18, 535-536. 

The ciystal structure of tantalum and niobium dioxyfluorides, Ta02F and Nb02F, consists of oxyfluoride octahedrons linked via their vertexes to form a three-dimensional lattice with a ReC>3 type structure, as demonstrated by Andersson and Astrom [233] and by Frevel and Rinn [234]. Fig. 39 shows the structure of Nb02F. 

Precipitated K-salt crystals are carefully filtrated and washed so as to separate them from the mother solution. Diying of filtrated K-salt is also a very delicate and important process that must be performed under conditions that avoid hydrolysis of the material. Potassium heptafluorotantalate is sensitive to water, basic compounds and alcohols, especially at elevated temperatures. The main product of K-salt hydrolysis is Marignac s salt. For a long time it was believed that the composition of Marignac s salt is K Ta F However, X-ray ciystal structure analysis and precise chemical analysis of the... 

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