Multiple-Quantum Cross-Polarization in MAS NMR of Quadrupolar Nuclei

Using Al-27 (I= 5/2) NMR of aluminium acetylacetonate, we show that it is possible to cross-polarize from a spin I=1/2 nucleus (H-1) directly to the central triple-quantum transition of a half-integer quadrupolar nucleus (Al-27) in a powdered sample under MAS conditions. The optimum conditions for this multiple-quantum cross-polarization (MQCP) are investigated experimentally and compared with existing theoretical results. The new technique is applied to the recently introduced two-dimensional MQMAS experiment for recording high-resolution NMR spectra of half-integer quadrupolar nuclei. (C) 1998 Elsevier Science B.V.