Distribution and Position of Cations in the Structure

The cations balancing the negative charge of the framework locate in the channels and cages of a zeolite structure. The number and sites of cations are of interest due to their 

Na+ Site name No./unit cell Site name No./unit cell Site description 

By using single-crystal X-ray diffraction, Olson determined the structure of dehydrated NaX [Na88 Al88Si104O384, Fd3, a0 = 25.099(5) A],[31] in which all theNa+ cations could be located. Table 2.4 summarizes the distribution of Na+ cations in Na88X. In each unit cell, the occupancy of Na+ is 2.9 for site I, 21.1 for site I, 31.0 for site II, and 29.8 for site III. Na+ on site I is split into two closely related sites, and on site III into three closely related sites. 

As seen from Table 2.4, the theoretical model agrees with the experimental results. 

In the view of structural chemistry, the distribution of cations is also affected by many other factors, such as size of the cage, distribution of the static electric field, radius of the cation, and hydration and dehydration states of the zeolites, etc. 

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