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

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 Na2SnO3.3H2O, Na2TeO4.2H2O, Na2SiO3.9H2O and NaBO2.2H2O 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.