NMR Crystallography of Aluminum Carbide: Impurities in the Reagent and Improved ²⁷Al NMR Tensors

The structure of aluminum carbide (from two different manufacturers) has been interrogated by ²⁷Al solid-state NMR in an effort to accurately characterize the material. Quadrupolar line shapes for ²⁷Al sites such as these are important to catalogue, as efforts are underway to employ NMR crystallography tools to understand and predict both solid-state structures and perturbations to these that are relevant to NMR analyses. Impurities present in both of the samples are revealed to be aluminum oxycarbides, as well as an aluminum metal impurity in one and aluminum nitride in another - potentially important information for groups employing aluminum carbide in syntheses or in other applications. Triple-quantum magic-angle spinning (3Q-MAS) ²⁷Al NMR was employed to help determine the quadrupolar parameters of the two crystallographically inequivalent aluminum sites in Al₄C₃. Revised values for the quadrupolar tensors of this material were measured and simulated through use of CASTEP-NMR.