Synthesis and crystal structures of Cs2MgD4 and Cs3MgD5

The title compounds were prepared by sintering stoichiometric mixtures of t he binary deuterides in an autoclave under 65 bar pressure at 625 K. Neutro n powder diffraction reveals a beta-K2SO4 type structure for Cs2MgD4 (space group Pmna, a = 8.5988(4), b = 6.6234(3), c = 11.5988(5) Angstrom) and a C s3CoCl5 type structure for Cs3MgD5 (space group I4/mcm, a = 8.4022(2), c = 12.6951(4) Angstrom). In both deuterides magnesium is tetrahedrally coordin ated by deuterium. The Mg-D bond distances (1.82-1.88 Angstrom in Cs2MgD4 a nd 1.84 Angstrom in Cs3MgD5) are longer by 0.02 Angstrom, on the average, t han those in the corresponding rubidium analogues. (C) 2000 Elsevier Scienc e S.A. All rights reserved.