High magnetic field solid-state NMR analyses by combining MAS, MQ-MAS, homo-nuclear and hetero-nuclear correlation experiments

A general strategy of structural analysis of alumina silicate by combining various solid-state NMR measurements such as single pulse, multi-quantum magic angle spinning, double-quantum homo-nuclear correlation under magic angle spinning (DQ-MAS), and cross-polarization hetero-nuclear correlation (CP-HETCOR) was evaluated with the aid of high magnetic field NMR (800 MHz for ¹H Larmor frequency) by using anorthite as a model material. The high magnetic field greatly enhanced resolution of ²⁷Al in single pulse, DQ-MAS, and even in triple-quantum magic angle spinning NMR spectra. The spatial proximities through dipolar couplings were probed by the DQ-MAS methods for homo-nuclear correlations between both ²⁷Al-²⁷Al and ²⁹Si-²⁹Si and by CP-HETCOR for hetero-nuclear correlations between ²⁷Al-²⁹Si in the anorthite framework. By combining various NMR methodologies, we elucidated detailed spatial correlations among various aluminum and silicon species in anorthite that was hard to be determined using conventional analytical methods at low magnetic field. Moreover, the presented approach is applicable to analyze other alumina-silicate minerals.