Sodalite cage atom distribution

Fig. 4 Stereoscopic view of sodalite cage atom distribution of nickel faujasite. Reproduced with permission from reference 17. (Copyright 1968 American Chemical Society)...

If there are two or more types of T-atoms and these are ordered (i.e. not randomly distributed over all T-siles), the ideal symmetry of the framework type is likely to be reduced. For example, Al and Si alternate in the framework structure of zeolite A (LTA). To illustrate the effect of this ordering on the symmetry, the LTA framework type with all nodes identical and with alternating nodes marked are shown in Figs. 20a and b, respectively. The lattice constant (repeat distance) a and one of the mirror planes for the former is shown in Fig. 20a. In Fig. 20b, the symmetry reduction dictated by the ordering of Si and Al is readily apparent. Two obvious effects of the alternation are that (I) the mirror planes between sodalite cages arc gone, and (2) the unit cell has to be doubled along each of the axes. Similar elfects are observed in other materials in which the T-aloms are ordered. 

The cations, M, are distributed over cation sites located in the supercages, the sodalite cages and the hexagonal prisms of the faujasite structure (ref.9). The SiCl4 molecule has access to the supercages only. When the number of supercage cations is compared to the number of A1 atoms that were actually... 

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