Residual dipolar couplings in MAS and MQMAS NMR spectra of quadrupolar nuclei

Abstract

We report the first observation of residual dipolar couplings in magic-angle-spinning (MAS) and multiple quantum magic-angle-spinning (MQMAS) NMR spectra of half-integer quadrupolar nuclei. In particular, the fine spectral splittings observed in the 11 B MAS spectrum of crystalline triethanolamine borate are attributed to the residual 11 B– 14 N dipolar coupling, which is not completely averaged by MAS. This interpretation is corroborated by the observation of an asymmetrical doublet in the 11 B MQMAS spectrum.