Resolving crystallographically nonequivalent

A few cases have come to light in which crystallographic nonequivalence of tetrahedral sites for silicon has been reflected in the 29Si MAS NMR spectra of zeolites. The most complex and the best resolved example is the spectrum of silicalite which was discussed in Section III,F another is the spectrum of the well-ordered natural zeolite scolecite (57), which contains two signals corresponding to nonequivalent Si(3 Al) units (see Fig. 23). The correctness of... 

NMR spectra of solids with the quality of high resolution can be achieved when the above mentioned line broadening phenomena are removed or at least considerably reduced. Only in these cases spectra can be obtained which enable, for example, crystallographically nonequivalent sites of a zeoiitic material framework to be resolved as individual resonance lines. High resolution NMR spectra of solids can be received by use of one or more experimental techniques described in the following ... 

Si MAS NMR allows identification of crystallographically nonequivalent Si sites in zeolites as these sites in chemically equivalent environments may have different chemical shifts [56], It has been found that the Si MAS NMR spectrum of aluminum-free zeolite ZSM-5 (silicalite) [57] exhibits at 295 K 20 well resolved lines (two with a threefold intensity), representing the 24 crystallographically inequivalent Si sites of the monoclinic form (Fig. 10). At 393 K only 10 lines exist in the spectrum (two with a double intensity), which correspond... 

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