Triple-quantum two-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 multiple-quantum coherences of half-integer quadrupolar nuclei was used to study Al-27 sites in crystalline samples of leucite (KAlSi2O6), anorthite (CaAl2Si2O8), and kyanite (Al2SiO5), as well as CaAl2Si2O8 glass and a magnesium aluminoborate glass. In the crystals, multiple sites are partially resolved and new results for isotropic chemical shifts and quadrupolar parameters are derived, using data collected at a single magnetic field. Data for both leucite and anorthite are consistent with previous results that correlate chemical shifts with mean intertetrahedral bond angle. Signal can be obtained from sites with quadrupolar coupling constants as large as 9 MHz, but intensities are reduced. In the aluminoborate glass, peaks for sites with different Al coordination numbers are well separated. The lack of such features in CaAl2Si2O8 glass rules out the presence of significant quantities of AlO5 and AlO6 groups.