HIGH-FIELD B-11 MAGIC-ANGLE SPINNING NMR CHARACTERIZATION OF BORON NITRIDES

High-field (14.0 T) B-11 magic-angle spinning NMR characterization of the major forms of boron nitride reveals differences between the cubic (c-BN) and hexagonal (h-BN) forms, in terms of both isotropic chemical shifts and magnitude of the second-order quadrupole contribution to observed NMR line shapes. B-11 NMR spectra of the pure turbostratic (t-BN) form and of t-BN in the form of an AIN/BN composite are indistinguishable from those of crystalline h-BN. This observation is in accord with the weak nature of the interplanar bonding interaction in t-BN. The results presented involving the structural characterization of boron nitrides by solid-state NMR should serve as a foundation for future studies involving pyrolytic conversion of organometallic and polymeric precursors to boron nitride.