On the preparation and structure of caesium aluminium tetrahydride

A new tetragonal phase of CsAlH₄ was observed after the precipitation of CsAlH₄ from a diglyme solution with an inert solvent. This new phase and the previously described orthorhombic phase were characterized by a combination of X-ray powder diffraction analysis and ²⁷Al and ¹³³Cs solid-state NMR spectroscopy. The transformation of the tetragonal CsAlH₄ phase into the orthorhombic CsAlH₄ phase can be induced by thermal treatment, whereas the opposite process can be stimulated by mechanical treatment. The phase transformation processes are almost completely reversible and can be performed several times without any observable decomposition of CsAlH₄. The structure of the tetragonal CsAlH₄ phase (space group I4₁/a) was solved from X-ray powder diffraction data, and the lattice parameters were determined to be a = 5.6732(4) and c = 14.2795(11) Aa. (Copyright copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)