Six-rings, double

Figure 2.10 Framework structure for FAU zeolite formed by linking sodalite cages through double six-rings.

Some vibrational modes of zeolites are sensitive to the amount of aluminum in the framework [93]. The substitution of aluminum for silicon atoms in the zeolite framework changes the T-O-T bond angles (where T is a tetrahedral atom that can be either Si or Al). This is primarily due to the smaller size and different charge density of the aluminum atoms compared to silicon. This results in a shift in frequency for vibrational modes in the zeolite due to external linkages. The T-O-T asymmetric (1100-980 cm ) and symmetric (800-600 cm ) stretching modes as well as structural unit vibrations Mke double four- and double six-rings exhibit a shift to lower frequencies as the aluminum content of the framework is increased. Figure 4.19 shows this relationship for a faujasite-type framework. 

Figure 4.19 Frequency dependence on mole fraction of framework aluminum for various vibrational modes ofX and Y zeolites. D6R means double six-ring, and Uj are the...

Flanigen monitored the changes in the IR spectra that occur during the synthesis of NaX zeolite from a sodium aluminosilicate gel. The appearance of absorption bands due to the formation of structural units in the zeoUte as the crystallization of NaX proceeded were observed [93]. In particular, the growth of a band around 575 cm indicated the formation of double six-rings which is one of the structural sub-units of X zeolite. 

Offretite and E also contain columns of gmellnite cages but have substantial numbers of double six rings (D6R). Molecular modelling... 

The zeolite X and Y framework is considered to be topologically built up out of basic units consisting of two sodalite cages that can be connected to other units through double six-rings into 6 directions. In this way, a three dimensional network of T-site connectivities can easily be constructed. Each unit contains 48 T-sites. Most calculations were done on a cluster of 27 (3x3x3) units, i.e., 1296 sites. 

Fig.1 Four typical structures of POSS cages a trigonal prismatic (SigOg) cage, b cubane (SisOn) cage, c double five-ring (SiioOis) cage, and d double six-ring (SinOis) cages...

C. S. Blackwell, J. Phys. Chem., 83, 3257 (1979). Investigation of Zeolite Frameworks by Vibrational Properties. 2. The Double-Six-Ring m Group 4 Zeolites. 

This was understood by realizing that the effect of the Al substitution will have twice the effect in site I (double six-ring) than in the single six-ring (sites I and II) and wall sites ("site III"). ... 

B. D. McNicol (Koninklijke/Shell Laboratorium, Amsterdam, Netherlands ) Would it be possible to use this technique to look at the induction period of zeolite crystal growth—e.g., identification of building units such as double six rings ... 

Yang, Y. Walawalkar, M. G. Pinkas. J. Roesky, H. W. Schmidt H.-G. Molecular alumlnophosphonate Model compound for the isoelectronic double-six-ring (D6R) secondary building unit of zeolites. Angew. Chem., Int. Ed. 1998, 37. 96—98. 

Figure 7. Projections of double six ring modes in siliceous faujasite on modes of molecular double six rings [14], is the square of the projection of the normalized vibrational displacement vector of the crystal on the normalized displacement vector of the molecule.

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