Zeolites have 3D framework structures based on the Si-O-Si links found in the silicates with some Al3+ cations replacing Si4+. Thus for each Al present there is often the equivalent of one positively charged mobile Group 1 ion in the structure. This can give rise to ion-exchange properties. The pictures of the Zeolites that are given in text books are often simplified to make the all important channel structures clearer. The most common simplification is to ignore the oxygens and to draw a bond between the Si atoms.
Zeolite-A The file za_icsd_38170.ins in \ortex can be used to examine the this structure. Use edit.INS to examine the INS file. The two Na ions and the Al have been suppressed by putting four spaces in front of the atom name. The Al is in the same position as the Si and it can be ignored. The Si and O atoms define the framework structure.
FVAR
O1 1 0.11330 0.11330 0.34440 11.00000 0.05000
O2 1 0.00000 0.22140 0.50000 11.00000 0.05000
O3 1 0.29130 0.29130 0.00000 11.00000 0.05000
Si1 1 0.37020 0.18640 0.00000 11.00000 0.05000
Al1 1 0.37020 0.18640 0.00000 11.00000 0.05000
Na1 1 0.24190 0.24190 0.17080 11.00000 0.05000
Na2 1 0.50000 0.40930 0.03970 11.00000 0.05000
HKLF 4
To see the framework structure open the INS file using Oscail and use ORTEX to pack two unit cells (atom based pack range 0 2, 0 1, 0 1).
This should give.
The crystal structure is cubic and has large channels running parallel to each axis.
The view down b is
and the view down a is
there are smaller connections between the large channels along the cell diagonals
Open the file za_cell_000.INS this contains a filled unit cell with the O atoms removed and the cell space group set to P1. If you set the covalent tolerance in ORTEX setup to 1.2 you should get the following picture
The file za_cell_000_110.INS contains two unit cells along the lattice diagonal
This looks like the typical Zeolite-A pictures in text books.
The building blocks are b-cages linked by cubes.
The program Void can be used to fill the voids in the framework with water sized spheres. The file za_2cell_void.INS was generated in this way. you can view the result using Pogl.
This is the view in Pogl with no atoms selected and void size set to 2.0.
Faujasite
The faujasite structure is more complex and is built up from b-cages linked by hexagonal prisms.
The file fau_frag.INS can be used to view the structure.
If you turn this around you should be able to see the diamond like linking of the b-cages.
Sodalite
The file sod_frag.INS can be used to view the sodalite framework.
The structure is cubic and is built up from b-cages alone aligned along the unit cell directions.
ZSM-5
The file zsm5_icsd_60674.INS contains the atoms of a zsm-5 structure. The non-framework atoms have been suppressed by the position of the HKLF 4 instruction. Packing this in ORTEX using an atom based pack range (-5. 1.5, 0 1, 0 1) should give the picture shown here.
The large cavity bisected by the z-axis is clearly seen.
The file zsm5_void.INS was generated using the program Void. Using ORTEX and Pogl the channels can be visualised.
Using ORTEX and Render/Raster 3D with the Void option selected in Render options gives the voids as transparent spheres;
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