Cubic CsCaH3 and hexagonal RbMgH3:: new examples of fluoride-related perovskite-type hydrides

The title compounds and their deuterides were synthesized by sintering stoichiometric mixtures of the binary hydrides (deuterides) at 675 K and 200 bar H-2 (D-2) for 10 days and characterized by X-ray and neutron powder diffraction. CsCaH3 crystallizes with the cubic perovskite structure, space group Pm (3) over bar m (221), a=4.6170(2) Angstrom (hydride), a=4.6093(2) Angstrom (deuteride). The distances (Cs-D: 3.26 Angstrom, Ca-D: 2.31 Angstrom, D-D: 3.26 Angstrom) are consistent with those found in Cs2CaH4. RbMgH3 is the first example of a metal hydride crystallizing with the BaTiO3 (6H variant of the hexagonal perovskite) structure, space group P6(3)/mmc (194), a=5.9030(1) Angstrom, c=14.3158(3) Angstrom (deuteride). The M-D distances (Rb-D: 2.96-3.03 Angstrom, Mg-D: 2.01-2.04 Angstrom) and shortest D-D distances (2.52 Angstrom) are in agreement with distances found in other deuterides. (C) 1999 Elsevier Science S.A. All rights reserved.