Synthesis, crystal structure and hydrogenation properties of the novel metal compound LaNi 2Mn 3

Abstract

LaNi 2Mn 3 has been synthesised from the elements and investigated with respect to crystal structure and hydrogenation properties. Single crystal X-ray diffraction reveals a YNi 2Al 3 type structure (space group P6/mmm, a=9.2099(9), c=4.1892(4) Å, c/ a=0.4548) that is distinctly different from the CaCu 5 type structure of LaNi 5. The compound absorbs reversibly up to six hydrogen atoms per formula unit near ambient conditions and shows a hydrogen plateau pressure of ∼1 bar near 60 °C. The hydrogen atoms in the expanded metal atom structure were localised by neutron powder diffraction on deuterides of composition LaNi 2Mn 3D 4.6 ( a=9.7125(2), c=4.3057(1) Å, c/ a=0.4433) and LaNi 2Mn 3D 5.6 ( a=9.8379(2), c=4.3038(1), c/ a=0.4375). They occupy one octahedral coordinated site [La 2Mn 4] with full occupancy and three tetrahedral coordinated sites [La 2Mn 2], [La 2NiMn] and [LaMn 2Ni], and a deformed square pyramidal coordinated site [LaMn 2Ni 2] with partial occupancies.