Double-quantum cross-polarization between half-integer quadrupolar spin systems:: 11B⇆23Na and 11B ⇆ 27Al

Cross-polarization/magic angle spinning (CPMAS) experiments are reported in which both the source and recipient spin systems an based on half-integer nuclei with strong second-order quadrupolar interactions. Double-quantum (DQ) CP is particularly well suited for this purpose, as demonstrated with B-11{Na-23} CPMAS spectra of sodium diborate. Furthermore, a two-dimensional B-11{Al-27} heteronuclear correlation spectrum is obtained on a magnesium aluminoborate glass, demonstrating preferential connectivities among various distinct boron and aluminum sites. Novel spectral editing opportunities arise from semi-selective coherence transfer rates measured by exploiting off-resonance effects on spin-locking efficiencies. (C) 1998 Elsevier Science B.V. All rights reserved.