Magic-angle spinning nuclear magnetic resonance of half-integer quadrupole nuclei: effect of spin-locking efficiency on powder lineshapes

Abstract

23Na spin-lock magic-angle spinning (MAS) and cross-polarization (CP) MAS nuclear magnetic resonance (NMR) spectra have been traced for sodium-containing compounds such as Na 2SnO 3·3H 2O, Na 2TeO 4·2H 2O, Na 2SiO 3·9H 2O and NaBO 2·2H 2O whose asymmetric factors in quadrupole interaction are 0.00, 0.37, 0.63 and 0.80, respectively. The lineshapes in the spin-lock/MAS and CP/MAS NMR spectra are different from those in the spectra measured with the single-pulse sequence (SP) combined with 1H dipolar decoupling (DD). In other words, the former lineshapes are distorted from the theoretical ones broadened by the second-order quadrupole interaction. The lineshapes are distorted during the spin-locking period, since the spin-locking efficiency depends on the crystallite orientation in a powder sample. We have discussed the distortion on theoretical bases and simulated the observed spectra.