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Synthesis, Crystal Structures and Thermal Properties of Ammine Barium Borohydrides

Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, Langelandsgade 140, DK-8000 Aarhus C, Denmark
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Received: 1 September 2020 / Revised: 30 September 2020 / Accepted: 6 October 2020 / Published: 10 October 2020
Ammine metal borohydrides show large compositional and structural diversity, and have been proposed as candidates for solid-state ammonia and hydrogen storage as well as fast cationic conductors. Here, we report the synthesis method of ammine barium borohydrides, Ba(BH4)2·xNH3 (x = 1, 2). The two new compounds were investigated with time-resolved temperature-varied in situ synchrotron radiation powder X-ray diffraction, thermal analysis, infrared spectroscopy and photographic analysis. The compound Ba(BH4)2·2NH3 crystallizes in an orthorhombic unit cell with space group symmetry Pnc2, and is isostructural to Sr(BH4)2·2NH3, forming octahedral [Ba(NH3)2(BH4)4] complexes, which are connected into a two-dimensional layered structure, where the layers are interconnected by dihydrogen bonds, N–Hδ+−δH–B. A new structure type is observed for Ba(BH4)2·NH3, which crystallizes in an orthorhombic unit cell with space group symmetry P212121, forming a three-dimensional framework structure of [Ba(NH3)(BH4)6] complexes. The structure is built from distorted hexagonal chains, where NH3 groups form dihydrogen bonds to the nearby BH4-groups within the chain. Ba(BH4)2·2NH3 is unstable at room temperature and releases NH3 in two subsequent endothermic reactions with maxima at 49 and 117 °C, eventually reforming Ba(BH4)2. We demonstrate that the thermal stability and composition of the gas release for the ammine alkaline earth metal borohydrides can be correlated to the charge density of the metal cation, but are also influenced by other effects. View Full-Text
Keywords: complex metal hydrides; ammine metal borohydrides; crystal structures complex metal hydrides; ammine metal borohydrides; crystal structures
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MDPI and ACS Style

Grinderslev, J.B.; Amdisen, M.B.; Jensen, T.R. Synthesis, Crystal Structures and Thermal Properties of Ammine Barium Borohydrides. Inorganics 2020, 8, 57. https://0-doi-org.brum.beds.ac.uk/10.3390/inorganics8100057

AMA Style

Grinderslev JB, Amdisen MB, Jensen TR. Synthesis, Crystal Structures and Thermal Properties of Ammine Barium Borohydrides. Inorganics. 2020; 8(10):57. https://0-doi-org.brum.beds.ac.uk/10.3390/inorganics8100057

Chicago/Turabian Style

Grinderslev, Jakob B., Mads B. Amdisen, and Torben R. Jensen 2020. "Synthesis, Crystal Structures and Thermal Properties of Ammine Barium Borohydrides" Inorganics 8, no. 10: 57. https://0-doi-org.brum.beds.ac.uk/10.3390/inorganics8100057

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