TRIPLE-QUANTUM 2-DIMENSIONAL AL-27 MAGIC-ANGLE-SPINNING NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPIC STUDY OF ALUMINOSILICATE AND ALUMINATE CRYSTALS AND GLASSES

A new two-dimensional magic-angle spinning NMR experiment(1,2) using m ultiple-quantum coherences of half-integer quadrupolar nuclei was used to study Al-27 sites in crystalline samples of leucite (KAlSi2O6), an orthite (CaAl2Si2O8), and kyanite (Al2SiO5), as well as CaAl2Si2O8 gla ss and a magnesium aluminoborate glass. In the crystals, multiple site s are partially resolved and new results for isotropic chemical shifts and quadrupolar parameters are derived, using data collected at a sin gle magnetic field. Data for both leucite and anorthite are consistent with previous results that correlate chemical shifts with mean intert etrahedral bond angle. Signal can be obtained from sites with quadrupo lar coupling constants as large as 9 MHz, but intensities are reduced. In the aluminoborate glass, peaks for sites with different Al coordin ation numbers are well separated. The lack of such features in CaAl2Si 2O8 glass rules out the presence of significant quantities of AlO5 and AlO6 groups.