Faujasite supercages

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

Freude et al. (169) carried out a systematic study of the relative amounts of four- and six-coordinated Al in thermally treated zeolite Y, using wide-line and MAS 27A1 NMR at 16 and 70.34 MHz, respectively. Table XV gives the results calculated per one faujasitic supercage ( of the unit cell). It is evident that loss of 27A1 line intensity takes place in treated zeolites in comparison with the parent material, evidently due to extra-framework Al being in an environment of low symmetry. 

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... 

Upon exposure of transition metal (Mn11, Fem, Cu11, Co11) exchanged zeolites to dicyanobenzene (DCB), encapsulated MePc complexes are formed in the faujasite supercages, according to the following stoichiometry ... 

An alternative method used for entrapment of large complexes into zeolite crystals is known as the so-called zeolite synthesis method .[67 701 In this method transition metal complexes are added to the synthesis mixture from which a faujasite zeolite is obtained. Therefore, the complex should be stable and dissolved in the medium in the conditions of zeolite synthesis, i.e. at elevated pH (> 12) and temperature (around 100 °C). It is not entirely clear whether occluded complexes are positioned in faujasite supercages or in cracks or defects of the crystals. To assure occlusion of isolated MePc complexes rather than of their clusters, the occluded amounts must be limited, implying the use of very active complexes. Ru and CoPcF17 complexes have been reported to show good activity and resistance to leaching.[67 701... 

The relative rates of carbenium ion reactions in faujasite supercages appear to follow a sequence type A /3-scission > type A alkyl shift > type Bi /3-scission > type B2 /3-scission > type B (PCP) isomerization > type C /3-scission (298). Normal alkanes, therefore, are transformed via the B-type (PCP) isomerization into branched isomers, which undergo /3-scission only after the creation of two or three side chains in the carbon skeleton. 

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. 

The La(H20)93+ at the Sn, and Sm sites of the faujasite supercage after initial exchange are subject to electrostatic interactions, and when the temperature is increased the La3+-H20... 

Domenech, A., Ferrer, B., Fomes, V., Garcia, H., and Leyva, A. 2005b. Ship-in-a-bottle synthesis of triphenylamine inside faujasite supercages and generation of the triphenylam-minium radical ion. Tetrahedron 61, 791-796. 

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... 

Although the mobility of MePc complexes should be strongly reduced in the intracrystalline faujasite supercages, truly site-isolated metal centers can be obtained this way. Moreover, Fc and Mn (salts or exchanged zeolites) which arc active for one-elcctron redox processes as in Fenton free radical H2O2 decomposition (see reaction),... 

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

The pore opening in faujasites is estimated to be ca. 8 A, while the large cavity, that is, the supercage or a-cage, is estimated to have a diameter of 13 A. Small molecules can readily enter the pores and large molecules can be synthesized within the supercage. Clusters such as Rh6(CO)i6 and the Schiff base complex, VO(saloph), can be prepared within the faujasite supercage. (Saloph =... 

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]. 

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... 

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