Structural studies of the hydrogen storage material Mg2NiH4. 1. Cubic high-temperature structure

The structure of the high-temperature modification of Mg/sub 2/NiD/sub 4/ has been determined from neutron powder diffraction data collected at 280/sup 0/C. It is face-centered cubic (space group Fm3m, with a = 6.507 (2) A) with the metal atoms occupying anti-fluorite positions and the D atoms surrounding the Ni atoms in a disordered configuration of yet unknown local symmetry. The average structure resembles the K/sub 2/PtCl/sub 6/ structure type. The average metal-deuterium distances are d(Ni-D) = 1.49 (3) A and d(Mg-D) = 2.305 (3) A.