Quantitative multiple-quantum magic-angle-spinning NMR spectroscopy of quadrupolar nuclei in solids

We describe a new approach for observation of multiple-quantum (MQ) NMR spectra of S=3/2 nuclei with magic-angle spinning (MAS). The new method employs the Rotation-induced Adiabatic Coherence Transfer (RIACT) that occurs between triple-quantum (3Q) and central-transition (1Q) coherences in S=3/2 systems. In contrast to currently available coherence-transfer techniques, RIACT is relatively insensitive to the magnitude of the quadrupole interaction for e(2)qQ/h less than or equal to MHz for both 3Q excitation and 3Q-to-1Q conversion. Thus, RIACT provides a means of extracting quantitative information about site populations from isotropic MQ NMR spectra. We illustrate the utility of the approach with Na-23 (S=3/2) MQ quantitative measurements of quadrupolar parameters, chemical shifts, and relative site populations for each of the crystallographically distinct sodium sites.