Concomitant Enhancement of the Reorientational Dynamics of the BH 4 – Anions and Mg 2+ Ionic Conductivity in Mg(BH 4 ) 2 ·NH 3 upon Ligand Incorporation
Year: 2025
Type: article
Abstract: High Resolution Image Download MS PowerPoint Slide The addition of neutral ligand NH 3 is known to increase the Mg 2+ ionic conductivity in Mg(BH 4 ) 2 ·NH 3 as compared to the parent compound Mg(BH 4 ) 2 . Using inelastic neutron scattering, quasielastic neutron scattering, synchrotron X-ray powder diffraction, impedance spectroscopy, and density functional theory, the structure, the dynamics, and the Mg 2+ ionic conductivity were investigated. The results show that the introduction of the NH 3 ligand not only enhances the Mg 2+ ionic conductivity but also significantly increases the reorientational mobility of the BH 4 – anions. Thus, the results suggest that there may be a link between the two. Furthermore, the results show that Mg(BH 4 ) 2 ·NH 3 exhibits two coordination environments for the BH 4 – anions, which act as either bridging or terminal anions, in contrast to Mg(BH 4 ) 2, which only exhibits bridging anions. The different coordination environments in Mg(BH 4 ) 2 ·NH 3 lead to a clear difference in dynamics where the terminal anions have a much lower reorientational energy barrier (∼65 meV), as compared to the bridging anions (∼280 meV), and thus become dynamically active at much lower temperatures. The results show that the NH 3 ligands also exhibit reorientational dynamics and that these are even faster than the dynamics of the BH 4 – anions, with the NH 3 ligands having a reorientational energy barrier of ∼10 meV. In addition to the reorientational dynamics, the NH 3 ligands undergo quantum mechanical rotational tunneling below 50 K. In summary, this study provides a detailed characterization of both the structure and the dynamics of Mg(BH 4 ) 2 ·NH 3 and suggests that the rapidly reorienting terminal BH 4 – anions may be behind the increased Mg 2+ ionic conductivity upon ligand incorporation.
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $4,500
Funders: National Science Foundation, Aarhus Universitet, Uddannelses- og Forskningsministeriet, Teknologi og Produktion, Det Frie Forskningsråd, Natur og Univers, Det Frie Forskningsråd, Göran Gustafssons Stiftelser, Vetenskapsrådet, Magnus Bergvalls Stiftelse, Stiftelsen Åforsk, DanScatt, National Institute of Standards and Technology
OpenAlex ID: W7117117102