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High-pressure structural changes in NaBH4·2H2O, observed up to 11 GPa through X-ray diffraction and Raman scattering spectroscopy, were analyzed to assess the influence of dihydrogen bonds on its crystal structure. At approximately 4.6 GPa, certain dihydrogen bonds were broken, leading to the decomposition of NaBH4·2H2O into ambient pressure phase of NaBH4 (α-NaBH4) and ice VII. Upon further compression beyond 6.6 GPa, NaBH4 gradually transformed into its high-pressure phase, γ-NaBH4. During decompression, γ-NaBH4 reverted to α-NaBH4 at the pressure between 4.4 and 2.7 GPa and subsequently reacted with ice VII, resulting in the recrystallization of NaBH4·2H2O. In addition, density functional theory calculations were used to evaluate the pressure dependence of hydrogen–hydrogen (H–H) distances in NaBH4·2H2O. As pressure increased, the number of dihydrogen bonds within the unit cell rose from five at near-ambient pressure to eleven at approximately 4 GPa, indicating that each hydrogen atom in the water molecule formed dihydrogen bonds with around three hydrogens from the BH4– ions just prior to dehydration.

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  This document is the Accepted Manuscript version of a Published Work that appeared in final form in Inorganic Chemistry, copyright © 2025 American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.inorgchem.4c04056.

Keyword: dihydrogen bond, sodium borohydride dihydrate, pressure-induced dehydration, sodium borohydride, ice VII, high-pressure, crystal structure

Date published: 2025-01-27

Publisher: American Chemical Society (ACS)

Journal:

• Inorganic Chemistry (ISSN: 00201669) vol. 64 issue. 3

Funding:

• Japan Society for the Promotion of Science JP18K05284
• Japan Society for the Promotion of Science JP21H00030
• Japan Society for the Promotion of Science JP23103706

Manuscript type: Author's version (Accepted manuscript)

MDR DOI: https://doi.org/10.48505/nims.5303

First published URL: https://doi.org/10.1021/acs.inorgchem.4c04056

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Updated at: 2025-01-28 10:41:51 +0900

Published on MDR: 2026-01-15 08:20:19 +0900