Faujasite supercage structure

FIGURE 1. Structure of the faujasite supercage (the arrows indicate the positions of the cations)... 

Where Cz characterizes Xe-surface collisions and p, is the probability factor depending only on the particular structure under consideration. The importance of Eq. (27) lies in the fact that its various terms can be determined separately. For example, ds + SE is obtained by extrapolation of the plot of chemical shift to zero pressure. It is found that 8B is negligible in zeolites Na-Y and H-Y, possibly because of motional averaging of electric field effects on the large faujasite supercages, but it becomes important in alkaline earth-exchanged forms. Zeolites Ca-A, Na-X, Na-Y, H-Y Ca-Y, L, mordenite, and ZSM-5 have been studied using the method because of the aperture size, xenon is not sorbed on zeolite Na-A. In synthetic faujasites, the chemical shift is a linear function of pressure and varies between 58 to 110 ppm (from Xe gas... 

From the structural viewpoint this is reasonable because the La(H20)93+ ion has a radius of 7.92 A, and the La(H20)93+ diffused into the faujasite supercages can only exchange the Na+ at the Sn and Sm sites. It is hard for this hydrated ion to pass through [> cage window to interact with the Na+ at the S site, or at 100 °C the reaction rate is very low. 

In the template method the zeolite is allowed to crystallize around the metal complex which is assumed to act as a structure directing agent, i.e. the bottle is built around the ship. This allows for the encapsulation of well-defined complexes without contamination by the fi-ee ligand or uncomplexed metal ions (see above). The method is restricted to metal complexes that are stable under the relatively harsh conditions of temperature and pH involved in hydrothermal synthesis. Balkus and coworkers [14,40,41] used this approach for the encapsulation of metallophthalocyanines in faujasite. However, in order to fit into the faujasite supercages the phthalocyanine ligands are strongly deformed and Jacobs has... 

Figure 4. Model of a platinum crystallite in a faujasite supercage exhibiting a host-guest orientation-relationship due to structural accomodation.

Various metal complexes such as metal phthalocyanines, metal salenes or Ru pyridyl complexes have been incorporated in molecular sieves such as cavity-structured zeolites (faujasites, supercages with 1.3-nm diameter), channel-structured aluminium phosphates (AIPO4-5, channel diameter 0.73 nm) and channel-structured silicates MCM-41 (channel diameter 3.2 nm) [51-53]. Different strategies were applied for the inclusion of the phthalocyanines. For example, whereas the zeolite-encaged phthalocyanines (1 R = -FI M = Co(II), Ru(II), etc.) are synthesized by the reaction of a transition metal ion-exchanged zeolite with phthalonitrile in a closed-bomb vessel [54], in the cases of AIPO4-5 and MCM-41 substituted derivatives of phthalocyanines were added to the mixture during the hydrothermal synthesis of the molecular sieve [55,56]. 

Figure 8-3. Molecular sieve zeolite faujasite. Left Structure of the zeolite with supercages of 1.3-tun diameter. Right Model for the incorporated metal phthalocyanine 1 (R = -H) with diameter 1.2 nm.

Various metal complexes such as metal-phthalocyanines, metal-salenes or Ru-pyridyl complexes were incorporated in molecular sieves such as cavity-structured zeolites (faujasites, supercages with 1.3 nm diameter), channel-structured aluminum phosphates... 

Zeolites X and Y have faujasite-like structure. The faujasite framework is an array of truncated, octahedra linked by D6R prisms. The supercage that is formed in this way is larger than that in zeolite A. These large cavities are accessible through distorted 12-ring windows of 0.8-0.9 nm diameter. The supercages are 1.2-1.3 nm diameter and can contain 2.8 isooctane or 5.4 benzene molecules [179] at 25°C. 

Recently, the PER of phenyl acetate and phenyl benzoate has been studied within zeolites of the faujasite and pentasil families, which are structurally very different. [277,278] It was found that for phenyl acetatet in faujasites X and Y, the predominating product is the ortho isomer, whereas in the pentasils ZSM-5 and ZSM-11, the preferred product is the para isomer. These differences have been explained taking into account the different sizes and shapes of the cavities and channels of the two families. The faujasites are made up of channels of 8 A diameter, leading to supercages of 13 A diameter, where the reaction is expected to occur, whereas the pentasils are made up of narrow channels of 6 A diameter. In the X and Y faujasites, the ortho position would be favored due to the restricted mobility, whereas in the channels of ZSM-5 and ZSM-11, there would be a shape limitation because the ortho isomer does not fit but the para isomer does (Table 15). With phenyl benzoate inside X or Y zeolites, the same... 

The topological structure of X- and Y-type zeolites (also known as faujasites) consists of an interconnected three-dimensional network of relatively large spherical cavities termed supercages (diameter of about 13 A Figure 12). Each supercage is connected tetrahedrally to four other super-... 

The open three-dimensional nature of zeolite structures permits diffusion of reactant molecules into the interior voids in the crystal and accounts for the high effective surface area of these materials. Faujasitic zeolites have channels of about 8-A diameter connecting cavities of 13-A diameter (supercages) in a three-dimensional network. The zeolite mor-denite has parallel channels with a diameter of about 7-A. The intracrystalline surface of the zeolite is, therefore, accessible to molecules with kinetic diameters equal to or smaller than the channel diameters. 

An X-ray structure analysis was carried out 179) on a single crystal of natural faujasite which had been exchanged with Cu2+ ions, dehydrated, and then exposed to butadiene. The major effect of adsorbing butadiene was to induce a migration of copper cations to site III, located at the pore entrances to the supercages (see Fig. 17). The unsaturated coordination of... 

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