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Issue 33, 2012
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The structure, thermal properties and phase transformations of the cubic polymorph of magnesium tetrahydroborate

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Abstract

The structure of the cubic polymorph of magnesium tetrahydroborate (γ-Mg(BH4)2) has been determined in space group Ia[3 with combining macron]d from a structural database of the isoelectronic compound SiO2; this has been corroborated by DFT calculations. The structure is found to concur with that recently determined by Filinchuk et al. (Y. Filinchuk, B. Richter, T. R. Jensen, V. Dmitriev, D. Chernyshov and H. Hagemann, Angew. Chem. Int. Ed., 2011, DOI: 10.1002/anie.201100675). The phase transformations and subsequent decomposition of γ-Mg(BH4)2 on heating have been ascertained from variable-temperature synchrotron X-ray diffraction data combined with thermogravimetric and mass spectrometry measurements. At ∼160 °C, conversion to a disordered variant of the β-Mg(BH4)2 phase (denoted as β′) is observed along with a further unidentified polymorph. There is evidence of amorphous phases during decomposition but there is no direct crystallographic indication of the existence of Mg(B12H12) or other intermediate Mg–B–H compounds. MgH2 and finally Mg are observed in the X-ray diffraction data after decomposition.

Graphical abstract: The structure, thermal properties and phase transformations of the cubic polymorph of magnesium tetrahydroborate

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Supplementary files

Article information


Submitted
31 Oct 2011
Accepted
29 Jun 2012
First published
25 Jul 2012

Phys. Chem. Chem. Phys., 2012,14, 11800-11807
Article type
Paper

The structure, thermal properties and phase transformations of the cubic polymorph of magnesium tetrahydroborate

W. I. F. David, S. K. Callear, M. O. Jones, P. C. Aeberhard, S. D. Culligan, A. H. Pohl, S. R. Johnson, K. R. Ryan, J. E. Parker, P. P. Edwards, C. J. Nuttall and A. Amieiro-Fonseca, Phys. Chem. Chem. Phys., 2012, 14, 11800
DOI: 10.1039/C2CP23439D

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