On the preparation and NMR spectroscopic characterization of potassium aluminium tetrahydride KAlH4

Abstract

Potassium aluminium tetrahydride KAlH₄ of high phase purity (space group Pnma (62)) was synthesized via a mechanochemical route. The thus obtained material was studied by ²⁷Al and ³⁹K MAS NMR spectroscopy. For both nuclei precise data for the isotropic chemical shift and the quadrupole coupling at T = 295 K were derived (²⁷Al: δ_iso = (107.6 ± 0.2) ppm, C_Q = (1.29 ± 0.02) MHz and η = 0.64 ± 0.02; ³⁹K: δ_iso = (6.1 ± 0.2) ppm, C_Q = (0.562 ± 0.005) MHz and η = 0.74 ± 0.02). The straightforward NMR spectroscopic approach applied here should also work for other complex aluminium hydrides and for many other materials containing half-integer nuclei experiencing small to medium-sized quadrupole couplings.