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Open AccessArticle

Covalent Si–H Bonds in the Zintl Phase Hydride CaSiH1+x (x ≤ 1/3)

1
Institute of Inorganic Chemistry, Leipzig University, Johannisallee 29, 04103 Leipzig, Germany
2
The ISIS Facility, STFC Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK
3
Institut Laue-Langevin, 71 avenue des Martyrs, 38000 Grenoble, France
4
Helmholtz-Zentrum Berlin, Hahn-Meitner-Platz 1, 14109 Berlin, Germany
*
Authors to whom correspondence should be addressed.
Dedicated to Prof. Dr. Joachim Sieler on the Occasion of his 80th Birthday.
Inorganics 2019, 7(9), 106; https://doi.org/10.3390/inorganics7090106
Received: 26 June 2019 / Revised: 1 August 2019 / Accepted: 7 August 2019 / Published: 21 August 2019
(This article belongs to the Special Issue Structure, Properties, and Bonding in Solid State Compounds)
The crystal structure of the Zintl phase hydride CaSiH≈4/3 was discussed controversially, especially with respect to the nature of the silicon-hydrogen interaction. We have applied X-ray and neutron powder diffraction as well as total neutron scattering on a deuterated sample, CaSiD1.1. Rietveld refinement (CaSiD1.1, Pnma, a = 14.579(4) Å, b = 3.8119(4) Å, c = 11.209(2) Å) and an analysis of the neutron pair distribution function show a silicon-deuterium bond length of 1.53 Å. The Si–H bond may thus be categorized as covalent and the main structural features described by a limiting ionic formula Ca2+H(Si)2/3(SiH)1/3. Hydrogen atoms decorating the ribbon-like silicon polyanion made of three connected zigzag chains are under-occupied, resulting in a composition CaSiH1.1. Hydrogen-poor Zintl phase hydrides CaSiH<1 with hydride ions in Ca4 tetrahedra only were found in an in situ neutron diffraction experiment at elevated temperature. Hydrogen (deuterium) uptake and release in CaSiDx (0.05 ≤ x ≤ 0.17) is a very fast process and takes less than 1 min to complete, which is of importance for possible hydrogen storage applications. View Full-Text
Keywords: Zintl phase; Zintl phase hydride; metal hydride; neutron diffraction; Rietveld refinement; pair distribution function; polyanions; hydrogen storage; silicon; in situ Zintl phase; Zintl phase hydride; metal hydride; neutron diffraction; Rietveld refinement; pair distribution function; polyanions; hydrogen storage; silicon; in situ
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MDPI and ACS Style

Auer, H.; Yang, F.; Playford, H.Y.; Hansen, T.C.; Franz, A.; Kohlmann, H. Covalent Si–H Bonds in the Zintl Phase Hydride CaSiH1+x (x ≤ 1/3). Inorganics 2019, 7, 106.

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