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Crystals 2019, 9(4), 193; https://doi.org/10.3390/cryst9040193

Hydrogenation Properties of LnAl2 (Ln = La, Eu, Yb), LaGa2, LaSi2 and the Crystal Structure of LaGa2H0.71(2)

1
Leipzig University, Institute of Inorganic Chemistry, Johannisallee 29, 04103 Leipzig, Germany
2
Leipzig University; Institute of Mineralogy, Crystallography and Materials Science, Scharnhorststraße 20, 04275 Leipzig, Germany
3
Leipzig University, Felix Bloch Institute for Solid State Physics, Linnéstraße 5, 04103 Leipzig, Germany
4
Helmholtz-Zentrum Berlin, Hahn-Meitner-Platz 1, 14109 Berlin, Germany
*
Author to whom correspondence should be addressed.
Received: 28 February 2019 / Revised: 24 March 2019 / Accepted: 26 March 2019 / Published: 3 April 2019
(This article belongs to the Section Crystalline Materials)
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Abstract

Many Zintl phases take up hydrogen and form hydrides. Hydrogen atoms occupy interstitial sites formed by alkali or alkaline earth metals and/or bind covalently to the polyanions. The latter is the case for polyanionic hydrides like SrTr2H2 (Tr = Al, Ga) with slightly puckered honeycomb-like polyanions decorated with hydrogen atoms. This study addresses the hydrogenation behavior of LnTr2, where the lanthanide metals Ln introduce one additional valence electron. Hydrogenation reactions were performed in autoclaves and followed by thermal analysis up to 5.0 MPa hydrogen gas pressure. Products were analyzed by powder X-ray and neutron diffraction, transmission electron microscopy, and NMR spectroscopy. Phases LnAl2 (Ln = La, Eu, Yb) decompose into binary hydrides and aluminium-rich intermetallics upon hydrogenation, while LaGa2 forms a ternary hydride LaGa2H0.71(2). Hydrogen atoms are statistically distributed over two kinds of trigonal-bipyramidal La3Ga2 interstitials with 67% and 4% occupancy, respectively. Ga-H distances (2.4992(2) Å) are considerably longer than in polyanionic hydrides and not indicative of covalent bonding. 2H solid-state NMR spectroscopy and theoretical calculations on Density Functional Theory (DFT) level confirm that LaGa2H0.7 is a typical interstitial metallic hydride. View Full-Text
Keywords: Zintl phases; metal hydrides; interstitial hydrides; Zintl phase hydrides; lanthanides; powder diffraction; neutron diffraction; deuterides; thermal analysis; solid-state NMR Zintl phases; metal hydrides; interstitial hydrides; Zintl phase hydrides; lanthanides; powder diffraction; neutron diffraction; deuterides; thermal analysis; solid-state NMR
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Werwein, A.; Benndorf, C.; Bertmer, M.; Franz, A.; Oeckler, O.; Kohlmann, H. Hydrogenation Properties of LnAl2 (Ln = La, Eu, Yb), LaGa2, LaSi2 and the Crystal Structure of LaGa2H0.71(2). Crystals 2019, 9, 193.

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