39K and 27Al NMR in potassium hydride and tetrahydridoaluminate

Polycrystalline potassium hydride KH and potassium tetrahydridoaluminate KAIH(4) were studied by K-39 and Al-27 NMR. Isotropic K-39 NMR chemical shifts at 292 K are +63(1) and -49(5) ppm (from aqueous 0.1 M KCI) in KH and KAIH(4), respectively. For KAIH4, the quadrupole coupling constant is C-Q(K-39) = 1.12(7) MHz and the asymmetry parameter is eta = 0.83(5). The Al-27 NMR spectra were analyzed with allowance for three states of the AlH4- anion in the lattice. For each of the states, the temperature dependence of C-Q(Al-27) is characterized by a negative slope : xi = 1/v(Q)(0) x partial derivativev(Q)/partial derivativeT congruent to -1 x 10(-4) K-1. The lattice distortions of AlH4-, depending on the cation, are related to the thermal stability of alkali-metal tetrahydridoaluminates.