MAGIC-ANGLE-SPINNING NUCLEAR-MAGNETIC-RESONANCE OF HALF-INTEGER QUADRUPOLE NUCLEI - EFFECT OF SPIN-LOCKING EFFICIENCY ON POWDER LINESHAPES

Na-23 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 H-1 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.