Framework structure determination single crystal diffraction

The determination of the structure of a zeolite with a new framework type remains a challenge to the powder method. Nonetheless, significant advances have been made in this area, and an increasing proportion of the new framework types are solved this way. While the techniques are rather sophisticated and beyond the scope of this chapter, it is perhaps important to know that methods of structure determination from powder diffraction data do exist and that all is not lost if single crystals of a new material cannot be synthesized. It may still be possible to solve the structure from the powder data [39,40,41]. 

The structures of compounds 55a,c and 56a,c were established by means of NMR spectroscopy and mass spectrometry. Due to the different polarity of the C=N and C=P triple bonds, the silicon ring atom in 55a,c is bound to the nitrogen atom, and in 56a,c to the carbon atom of the C=P moiety. The molecular structure of 55a was further determined by single-crystal X-ray diffraction analysis (Fig. 16).14 The four-membered SiNAsC framework is slightly puckered (folding angle N—Si—C/Si—C—As 7°), and... 

Among the over thirty framework compounds, at least 6 have been structurally determined by means of single crystal X-ray diffraction. These include GaP04-C3, -C4, -C7, AIASO4-I, -2 and GaAs04-2. The details of the cell parameters and the primary building units (PBU) of their structures are given in Table 4. 

Aluminum placement in ZSM-5 In ZSM-5 a key question is "Which of the 12 crystallographically independent sites accommodate the framework aluminum content " Reasonably accurate determinations of the crystal structures of a series of MFI-framework materials have been reported. At the low aluminum concentrations typical of ZSM-5 it has proved as yet impossible to measure experimentally the distribution of aluminum over the set of 12 crystallographically distinct T-sites in the structure of orthorhombic symmetry. Powder X-ray diffraction experiments have not jtielded information about aluminum placement. Large, quality single crystals are... 

Two octamolybdenum compounds, containing both bridging pyrazolate and terminal pyrazole ligands, [Mo8(pz)6(0),8(Hpz)6], 177, and [Mo8(pz)6-(0)2,(Hpz)6], 178, were prepared by the reaction of molten pyrazole with molybdenum oxides and their structures were determined by single-crystal X-ray diffraction (133). The overall geometries of 177 and 178 are similar. Both complexes consist of an octametallic framework that may be described as two bas-ally connected flattered trigonal pyramids. 

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