Building units of faulted zeolite framework structures and their simplest ordered end-member structures
1. The Periodic Building
Unit -
2. Type of faulting
- 3. The rod symmetry - 4.
Connectivity pattern of PBU -
5.
Simplest ordered end-members - 6. Materials
synthesized - 7. Supplementary material - 8.
References
1. The Periodic Building Unit (PBU) equals the chain shown in Fig. (a) :
The PBU of the decasil family of structures, is formed by connecting T12-Units (in bold) related by pure translations along c. As orientation sensitive indicator one of the T4-rings is shaded. The numbered T atoms are used in describing the connection modes. A perspective and parallel view down the chain axis is shown in (b).
2. Type of faulting: 2-dimensional stacking disorder of the PBUs along [100] and [010].
3. The rod symmetry (2/m) is indicated in the Figure.
4. Connectivity pattern of the PBU.
Neighboring PBUs can be connected via O-bridges in several ways:
The connection modes 2 and 3, 5 and 7 , and 6 and 8 are pairwise identical. The modes in each pair are related by a 1800 rotation about an axis parallel to the connecting TOT bridges.
Once the distribution of the connection modes in two dimensions is known, the 3-dimensional framework is defined.
5. The simplest ordered
end-members in the decasil family are given below.
Only
end-member 1 has been observed as single crystal material and
represents the structure type with code RTE (1,2).
|
End-Member |
Sequence of the
Connection Modes along a and b: |
Space Group Symmetry |
|
1 |
(5,5,....;7,7,.....) |
C2/m * |
|
2 |
(7,7....;8,6,8,...) |
P2/m |
|
3 |
(8,6,8,...;8,6,8,...) |
P4/m mm |
* This is the end-member with structure type code RTE (1,2); the sequence of the connection modes is along (-a + b) and (a + b), respectively.
6. Faulted structures synthesized so far:
RUB-4 (1,3)
The theory of the diffraction for the decasil family of structures is derived and discussed with respect to the existing materials RUB-3 and RUB-4. Simulated diffraction pattern of materials with different degree of disorder are presented and compared to experimental data from single crystal photographs (4).
A set of experimental powder diffraction diagrams for RUB-3(2) and
RUB-4(3) is given .
(1) B. Marler, A. Grünewald-Lüke, H. Gies: Zeolites 15, 388 (1995).
(2) B. Marler, A. Grünewald-Lüke, H. Gies: Micrporous Mesoporous Materials, in press.
(3) A. Grünewald-Lüke and H. Gies: Microporous Mater. 3, 159 (1994).
(4) P. Daniels: J. Appl. Cryst. 31, 559 (1998).
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