B NMR of Zeolites

B mas NMR spectrum of fully hydrated boralite. C. Two-dimensional B nutation spectrum of partially dehydrated boralite showing the weak presence of BO4 groups. The corresponding B mas NMR spectrum is shown above. From Axon and Klinowski (1994) by permission of the American Chemical Society. 

Compounds with structures related to ZrP207 show unique negative isotropic thermal expansion over a broad temperature range up to at least 950°C. The P MAS NMR 

Peak three corresponds to the equivalent P atoms of the P2O7 unit, the other four peaks correspond to the two inequivalent PO4 units, each split by its proximity to two configurations of the P2O7 unit which differ in the position of the bridging oxygen. B. 2D double-quantum P spectrum demonstrating the connectivity between two equivalent coupled P nuclei (P2O7 unit) with the same chemical shift (— 18.6 ppm). The fl2 dimension is the 2D spectrum filtered by the double quantum, the fl] dimension is the double quantum spectrum. From Pichot et al. (2001) by permission of Elsevier Science. 

The cation distributions in solid solutions Zn3-xMgx(P04)2 for x ranging from 0 to 3.0 have been studied by P MAS NMR (Jakeman et al. 1985). For values of x 1, four phosphorus sites could be distinguished, the relative intensities of which allowed the distribution of the cations to be calculated at each composition. 

Structural details of two related magnesium phosphates phosphoellenbergerite and holtedahlite have been determined by P MAS and CP MAS NMR, together with H NMR (Brunet and Schaller 1996). Both minerals contain protonated and unprotonated PO4 tetrahedra, identified with P resonances at —7.0 to —8.7 ppm and 1 to —4 ppm respectively. These assignments were confirmed by CP NMR measurements from which the relative intensities of the protonated and non-protonated tetrahedra were also determined. The NMR measurements were thus able to detect and characterise sites containing too small a proportion of the total protons to study by X-ray diffraction techniques (Brunet and Schaller 1996). 

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