PULSED-FIELD GRADIENT MULTIPLE-QUANTUM MAS NMR-SPECTROSCOPY OF HALF-INTEGER SPIN QUADRUPOLAR NUCLEI

Pulsed field gradients (PFGs) have been applied to select coherence tr ansfer pathways in multiple-quantum (MQ) MAS NMR spectra of half-integ er spin quadrupolar nuclei in rigid solids. Al-27 triple-quantum (3Q) MAS NMR spectra of the aluminophosphate molecular sieves VPI-5 and AlP O4-18 have been used to demonstrate the selection of the (0) --> (3) - -> (-1) coherence transfer pathway using PFGs and no phase cycling. Co mpared to MQMAS experiments that employ phase cycling schemes, the mai n advantage of the PFG-MQMAS technique is its simplicity, which should facilitate the combination of MQMAS with other pulse sequences. (C) 1 997 Elsevier Science B.V.