K-39 and Al-27 NMR in potassium hydride and tetrahydridoaluminate

Polycrystalline potassium hydride KH and potassium tetrahydridoaluminate KA IH(4) were studied by K-39 and Al-27 NMR. Isotropic K-39 NMR chemical shift s at 292 K are +63(1) and -49(5) ppm (from aqueous 0.1 M KCI) in KH and KAI H(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 i n 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 deriva tivev(Q)/partial derivativeT congruent to -1 x 10(-4) K-1. The lattice dist ortions of AlH4-, depending on the cation, are related to the thermal stabi lity of alkali-metal tetrahydridoaluminates.