Abstract
Yb 4Mg 4Fe 3H 22 and its deuteride were prepared by sintering mixtures of YbMg, Fe and LiH (LiD) powders in the ratio YbMg:Fe:LiH (LiD) = 4:3:1 at 510–520 °C and 120–155 bar hydrogen (deuterium) pressure, and were characterized by X-ray and neutron powder diffraction. They crystallize with cubic symmetry (space group, P4/ mmm; hydride, a = 6.6936(4) A ̊ ; deuteride, a = 6.6839(5) A ̊ , and are isostructural with the calcium analogue Ca 4Mg 4Fe 3H 22. The deuteride contains octahedral [FeD 6] 4− complex anions with bond distances [ Fe-4 D1] = 1.586(5) A ̊ and [ Fe-2 D2] = 1.554(7) A ̊ and tetrahedrally coordinated D − anions with bond distances [ D3- Mg] = 1.915(9) A ̊ and [ D3-3 Yb] = 2.411(7) A ̊ . At a hydrogen pressure of 6 bar, the Yb compound decomposes at about 480 °C into YbH 2, Mg and Fe, whereas the Ca analogue decomposes at about 450 °C into Ca 2FeH 6, Mg and Fe. The enthalpies of desorption, as measured from pressure-composition isotherms, are 137(3) kJ (mol H 2) −1 for Yb 4Mg 4Fe 3H 22 and 122(4) kJ (mol H 2) − for Ca 4Mg 4Fe 3H 22.
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