Synthesis and crystal structure of BaMgH4: A centrosymmetric variant of SrMgH4

BaMgH4 and its deuteride were synthesized by sintering 1:1 mixtures of BaH2 (BaD2) and Mg powder at 873 K and 200 bar hydrogen (deuterium) pressure for 10 days, and these were characterized by X-ray and neutron powder diffraction. They crystallize with the orthorhombic LaNiD4 structure type, space group Cmcm (No. 63), cell parameters at 295 K, hydride: a = 4.2109(2) Angstrom, b = 13.7672(8) Angstrom, c = 5.6984(3) Angstrom, V = 330.35(3) Angstrom(3); deuteride: a = 4.1992(1) Angstrom, b = 13.7374(5) Angstrom, c = 5.6852(2) Angstrom, V = 327.96(2) Angstrom(3); Z = 4. The structure contains one barium and one magnesium site having 13 (Ba) and 6 (Mg) deuterium neighbors and three deuterium sites which are four-, five- and sixfold coordinated, respectively. The metal-deuterium distances are in the range 2.66-3.16 Angstrom (Ba-D) and 1.87-2.11 Angstrom (Mg-D). The shortest D-D distance is 2.59 Angstrom. (C) 1997 Elsevier Science S.A.