Review and outlook
Ultra-wide line solid state NMR of quadrupolar nuclei: example of strontium-87

This article reviews the main features of solid-phase NMR as applied to the study of quadrupolar nuclei (I > 1/2). We emphasized the difficulties inherent in the study of such nuclei: lines greatly broadened by quadrupolar interaction at 1^er and 2^nd order, sensitivity, instrumental problems linked to reduced excitation ranges.

In the particular case of quadrupole interaction at 2^nd order, we have shown that MAS rotation does not allow complete averaging (even at infinite rotation frequency). Residual line broadening can be problematic in structural studies when several crystallographically inequivalent sites are present. High-resolution spectra can be obtained by implementing more complex macroscopic reorientations of the sample (DOR, DAS) or by manipulating the MQ transitions of the spin system (MQ-MAS). The MQ-MAS sequence has become a routine laboratory...