Four-rings, double

As mentioned in Section 4.2 earlier in this chapter, infrared spectroscopy was used to provide information about the structural units present in UZM-5. The framework IR spectrum of a UZM-5 sample is shown in Figure 4.18. The characteristic vibrational bands for double four-rings (D4R) and pentasil rings (S5) are present. This provided some valuable information about the types of linkage units present and combined with data from other techniques such as XRD and TEM allowed the structure of UZM-5 to be solved. 

Figure 4.18 Framework spectrum five-ring, D4R-double four-ring.

Figure 4.21 IR spectra of solids isolated at various times during a LTA synthesis. D4R refers to a double four-ring structural linkage.

FIGURE 2. Structures of silsesquioxanes. Left ladder structure middle double four-ring (= cubic octamer) right partial cage structure... 

Once bonded to the aluminate group, such large species may well wrap themselves around the central aluminium and react further this is consistent with the observation that the peaks assigned to AI(2Si) and AI(3Si) are always more intense than the Al(1 Si) peak (Figure 5). In this way, the aluminate reacts without breaking Si-O-Si bonds, consistent with Hoebbel s (16) observation on the formation of double-four-ring aluminosilicates. 

It has also been observed that zeolite A (10,11,12) and Losod (7) both with Si/Al = 1 have chemical shifts of -88.9 ppm, outside of the range proposed for Si-4A1. At first, this was attributed to S1-3A1 ordering in violation of Lowenstein s rule. However, recent neutron diffraction work on zeolite A (14) and NMR studies of its high silica analogue ZK-4, (8,13) have shown that the single resonance in zeolite A does correspond to S1-4A1. The unusual chemical shift for zeolite A may be a consequence of the strained double four rings in the structure and the presence of one nearly linear T-O-T angle. 

C. S. Blackwell, J. Phys. Chem., 83, 3251 (1979). Investigation of Zeolite Frameworks by Vibrational Properties. 1. The Double-Four-Ring in Group 3 Zeolites. 

B) Ion-exchange of silicate oligomers with Br and OH" to form inorganic-organic aggregates. (C) Self-assembly of SLC meso-phases. D4R = double four ring SLC = silicatropic liquid crystal. 

In the structures of several other microporous solids, including porosils, AlPOs and GaPOs, that were synthesized by the fluoride method, the fluoride anion was found in a different location than in [Co(cp)2]-NON, i.e., not directly bonded to one of the framework atoms. Instead, it occupies the center of a double four-ring unit. An example is another porosil of AST structure, namely quinuclidinium-AST [53]. Therefore, it has been supposed that the F" anion acts as a co-template, stabilizing structures that contain double four-ring units [23]. In agreement with this idea, we find that AST is only formed in fluoride-containing syntheses, and not in fluoride-fi-ee preparations. 

C.M. Draznieks, S. Girard, and G. Ferey, Novel Inorganic Frameworks constructed from Double-four-ring (D4R) Units Computational Design, Structures, and Lattice Energies of Silicate, Aluminophosphate, and Gallophosphate Candidates. J. Am. Chem. Soc., 2002, 124, 15326-15335. 

---