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| Autori principali: | , , , , , |
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| Natura: | Preprint |
| Pubblicazione: |
2025
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| Soggetti: | |
| Accesso online: | https://arxiv.org/abs/2508.03874 |
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| _version_ | 1866915431674019840 |
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| author | Nagle-Cocco, Liam A. V. Schneemann, Andreas Stone, Kevin H. Stavila, Vitalie Gennett, Thomas Strange, Nicholas A. |
| author_facet | Nagle-Cocco, Liam A. V. Schneemann, Andreas Stone, Kevin H. Stavila, Vitalie Gennett, Thomas Strange, Nicholas A. |
| contents | Hexammine magnesium borohydride, Mg(NH$_3$)$_6$(BH$_4$)$_2$, consists of adducted NH$_3$ molecules locked in a matrix of Mg cations and borohydride anions. It is a candidate material for hydrogen storage, with 16.8wt\% hydrogen stored in both the NH$_3$ and borohydride anions. It also may be of interest as a Mg$^{2+}$ conducting electrolyte in solid state batteries. Its crystal structure has, until now, eluded a proper structural solution due to ambiguity regarding the NH$_3$ position and behaviour. In this work, we show using synchrotron X-ray diffraction that the room-temperature structure can be solved only with a model assuming orientational disorder of ammonia molecules within the crystal structure. Cooling the sample to 120\,K yields additional Bragg peaks, which can only be solved with a unit cell expansion consistent with a freezing of the orientational freedom of ammonia molecules. Using this insight from the structure solution, we perform a full assignment of the vibrational modes in the room-temperature IR spectrum. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2508_03874 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Orientational Disorder of NH$_3$ in Hexammine Magnesium Borohydride Nagle-Cocco, Liam A. V. Schneemann, Andreas Stone, Kevin H. Stavila, Vitalie Gennett, Thomas Strange, Nicholas A. Materials Science Chemical Physics Hexammine magnesium borohydride, Mg(NH$_3$)$_6$(BH$_4$)$_2$, consists of adducted NH$_3$ molecules locked in a matrix of Mg cations and borohydride anions. It is a candidate material for hydrogen storage, with 16.8wt\% hydrogen stored in both the NH$_3$ and borohydride anions. It also may be of interest as a Mg$^{2+}$ conducting electrolyte in solid state batteries. Its crystal structure has, until now, eluded a proper structural solution due to ambiguity regarding the NH$_3$ position and behaviour. In this work, we show using synchrotron X-ray diffraction that the room-temperature structure can be solved only with a model assuming orientational disorder of ammonia molecules within the crystal structure. Cooling the sample to 120\,K yields additional Bragg peaks, which can only be solved with a unit cell expansion consistent with a freezing of the orientational freedom of ammonia molecules. Using this insight from the structure solution, we perform a full assignment of the vibrational modes in the room-temperature IR spectrum. |
| title | Orientational Disorder of NH$_3$ in Hexammine Magnesium Borohydride |
| topic | Materials Science Chemical Physics |
| url | https://arxiv.org/abs/2508.03874 |