A practical guide to solid-state NMR of half-integer quadrupolar nuclei with some applications to disordered systems

The practical aspects for obtaining useful NMR spectra of half-integer quadrupolar nuclei in diamagnetic solids are discussed in some detail. The general appearance of the Magic-Angle Spinning (MAS) line shape is described. The effects of a distribution in isotropic chemical shift and quadrupole interaction on the MAS line shape is shown. The necessity of fast MAS and short excitation pulses is demonstrated. The possibilities of ²⁷Al MAS NMR at high fields is shown for some clay minerals. Techniques to obtain spectra free of quadrupolar broadening, such as DOuble Rotation (DOR), Dynamic Angle Spinning WAS) and Multiple-Quantum Magic-Angle Spinning (MQMAS), are discussed with some emphasis on the newly developed MQMAS method. The latter is used to describe structural details of phosphorus-impregnated alumina and aluminosilicate sol-gel materials. These examples give a good indication of the capabilities of this new technique.