Abstract
Cross-polarization from ¹H to the multiple-quantum coherences of a quadrupolar nucleus is used in combination with the two-dimensional multiple-quantum magic angle spinning (MQMAS) NMR experiment in order to extract high-resolution CPMAS NMR spectra. The technique is demonstrated on ²³Na (S = 3/2), ¹⁷O, ²⁷Al (both S = 5/2) and ⁴⁵Sc (S = 7/2) nuclei, showing the applicability of multiple-quantum cross-polarization (MQCP) to systems with differing spin quantum number, gyromagnetic ratio, and relative nuclide abundance. The utility of this two-dimensional MAS NMR experiment for spectral editing and site-specific measurement of cross-polarization intensities is demonstrated. The possibility of direct cross-polarization to higher-order multiple-quantum coherences is also considered and three-, five- and seven-quantum cross-polarized ⁴⁵Sc MAS NMR spectra are presented.

Two-dimensional (a) three-quantum 17O MAS and (b) three-quantum cross-polarized 17O MAS NMR spectra of 35% isotopically enriched boehmite, recorded with (a) a three-quantum z-filtered experiment and (b) the three-quantum cross-polarized z-filtered experiment.