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

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 Al-27 and K-39 MAS NMR spectroscopy. For both nuclei precise data for the isotropic chemical shift and the quadrupole coupling at T = 295 K were derived (Al-27: delta(iso) = (107.6 +/- 0.2) ppm, C-Q = (1.29 +/- 0.02) MHz and eta = 0.64 +/- 0.02; K-39: delta(iso) = (6.1 +/- 0.2) ppm, C-Q = (0.562 +/- 0.005) MHz and eta = 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.