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| Home > Publications database > Synthesis of BaSiH$_6$ Hydridosilicate at High Pressures─A Bridge to BaSiH$_8$ Polyhydride |
| Home > Publications database > Synthesis of BaSiH$_6$ Hydridosilicate at High Pressures─A Bridge to BaSiH$_8$ Polyhydride |
| Journal Article | PUBDB-2025-01505 |
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2025
ACS Publications
Washington, DC
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Please use a persistent id in citations: doi:10.1021/acsomega.4c10502 doi:10.3204/PUBDB-2025-01505
Abstract: Hydridosilicates featuring SiH$_6$ octahedral moieties represent a rather new class of compounds with potential properties relating to hydrogen storage and hydride ion conductivity. Here, we report on the new representative BaSiH$_6$ which was obtained from reacting the Zintl phase hydride BaSiH∼$_{1.8}$ with H$_2$ fluid at pressures above 4 GPa and subsequent decompression to ambient pressure. Its monoclinic crystal structure (C2/c, a = 8.5976(3) Å, b = 4.8548(2) Å, c = 8.7330(4) Å, β = 107.92(1)°, Z = 4) was characterized by a combination of synchrotron radiation powder X-ray diffraction, neutron powder diffraction, and DFT calculations. It consists of complex SiH$_6$$^{2–}$ ions (d$_{Si–H}$ ≈ 1.61 Å), which are octahedrally coordinated by Ba${2+}$ counterions. The arrangement of Ba and Si atoms deviates only slightly from an ideal fcc NaCl structure with a ≈ 7 Å. IR and Raman spectroscopy showed SiH$_6$$^{2–}$ bending and stretching modes in the ranges 800–1200 and 1400–1800 cm$^{–1}$, respectively, in agreement with a hypervalent Si–H bonding situation. BaSiH$_6$ is thermally stable up to 95 °C above which decomposition into BaH$_2$ and Si takes place. DFT calculations indicated a direct band gap of 2.5 eV and confirmed that at ambient pressure BaSiH$_6$ is a thermodynamically stable compound in the ternary Ba–Si–H system. The discovery of BaSiH$_6$ consolidates the compound class of hydridosilicates, accessible from hydrogenations of silicides at gigapascal pressures (<10 GPa). The structural properties of BaSiH$_6$ suggest that it presents an intermediate (or precursor) for further hydrogenation at considerably higher pressures to the predicted superconducting polyhydride BaSiH$_8$ [Lucrezi, R.; et al. npj Comput. Mater. 2022, 8, 119] whose structure is also based on a NaCl arrangement of Ba and Si atoms but with Si in a cubic environment of H.
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