Covalent Si–H Bonds in the Zintl Phase Hydride CaSiH<sub>1+<i>x</i></sub> (<i>x</i> ≤ 1/3)
oleh: Henry Auer, Fangshun Yang, Helen Y. Playford, Thomas C. Hansen, Alexandra Franz, Holger Kohlmann
| Format: | Article |
|---|---|
| Diterbitkan: | MDPI AG 2019-08-01 |
Deskripsi
The crystal structure of the Zintl phase hydride CaSiH<sub>≈4/3</sub> 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, CaSiD<sub>1.1</sub>. Rietveld refinement (CaSiD<sub>1.1</sub>, <i>Pnma</i>, <i>a</i> = 14.579(4) Å, <i>b</i> = 3.8119(4) Å, <i>c</i> = 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 Ca<sup>2+</sup>H<sup>−</sup>(Si<sup>−</sup>)<sub>2/3</sub>(SiH<sup>−</sup>)<sub>1/3</sub>. Hydrogen atoms decorating the ribbon-like silicon polyanion made of three connected zigzag chains are under-occupied, resulting in a composition CaSiH<sub>1.1</sub>. Hydrogen-poor Zintl phase hydrides CaSiH<sub><1</sub> with hydride ions in Ca<sub>4</sub> tetrahedra only were found in an in situ neutron diffraction experiment at elevated temperature. Hydrogen (deuterium) uptake and release in CaSiD<i><sub>x</sub></i> (0.05 ≤ <i>x</i> ≤ 0.17) is a very fast process and takes less than 1 min to complete, which is of importance for possible hydrogen storage applications.