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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Mg(BH3)2 by Materials Project

Mg(BH3)2 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are four inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded in a 5-coordinate geometry to seven H+0.67+ atoms. There are a spread of Mg–H bond distances ranging from 2.00–2.30 Å. In the second Mg2+ site, Mg2+ is bonded in a 6-coordinate geometry to six H+0.67+ atoms. There are a spread of Mg–H bond distances ranging from 1.95–2.17 Å. In the third Mg2+ site, Mg2+ is bonded in a 6-coordinate geometry to six H+0.67+ atoms. There are a spread of Mg–H bond distances ranging from 1.98–2.04 Å. In the fourth Mg2+ site, Mg2+ is bonded in a 6-coordinate geometry to six H+0.67+ atoms. There are a spread of Mg–H bond distances ranging from 2.00–2.08 Å. There are eight inequivalent B3- sites. In the first B3- site, B3- is bonded in a distorted trigonal non-coplanar geometry to three H+0.67+ atoms. There are a spread of B–H bond distances ranging from 1.22–1.25 Å. In the second B3- site, B3- is bonded in a distorted trigonal non-coplanar geometry to three H+0.67+ atoms. There is one shorter (1.23 Å) and two longer (1.24 Å) B–H bond length. In the third B3- site, B3- is bonded in a distorted trigonal non-coplanar geometry to three H+0.67+ atoms. There are a spread of B–H bond distances ranging from 1.22–1.25 Å. In the fourth B3- site, B3- is bonded in a distorted trigonal non-coplanar geometry to three H+0.67+ atoms. There are a spread of B–H bond distances ranging from 1.23–1.25 Å. In the fifth B3- site, B3- is bonded in a distorted trigonal non-coplanar geometry to three H+0.67+ atoms. There are a spread of B–H bond distances ranging from 1.23–1.25 Å. In the sixth B3- site, B3- is bonded in a distorted trigonal non-coplanar geometry to three H+0.67+ atoms. There are a spread of B–H bond distances ranging from 1.22–1.25 Å. In the seventh B3- site, B3- is bonded in a distorted trigonal non-coplanar geometry to three H+0.67+ atoms. All B–H bond lengths are 1.24 Å. In the eighth B3- site, B3- is bonded in a distorted trigonal non-coplanar geometry to three H+0.67+ atoms. There are a spread of B–H bond distances ranging from 1.22–1.25 Å. There are twenty-four inequivalent H+0.67+ sites. In the first H+0.67+ site, H+0.67+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the second H+0.67+ site, H+0.67+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the third H+0.67+ site, H+0.67+ is bonded in a distorted L-shaped geometry to one Mg2+ and one B3- atom. In the fourth H+0.67+ site, H+0.67+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the fifth H+0.67+ site, H+0.67+ is bonded in a 2-coordinate geometry to two Mg2+ and one B3- atom. In the sixth H+0.67+ site, H+0.67+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the seventh H+0.67+ site, H+0.67+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the eighth H+0.67+ site, H+0.67+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the ninth H+0.67+ site, H+0.67+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the tenth H+0.67+ site, H+0.67+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the eleventh H+0.67+ site, H+0.67+ is bonded in a distorted L-shaped geometry to one Mg2+ and one B3- atom. In the twelfth H+0.67+ site, H+0.67+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the thirteenth H+0.67+ site, H+0.67+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the fourteenth H+0.67+ site, H+0.67+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the fifteenth H+0.67+ site, H+0.67+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the sixteenth H+0.67+ site, H+0.67+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the seventeenth H+0.67+ site, H+0.67+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the eighteenth H+0.67+ site, H+0.67+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the nineteenth H+0.67+ site, H+0.67+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the twentieth H+0.67+ site, H+0.67+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the twenty-first H+0.67+ site, H+0.67+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the twenty-second H+0.67+ site, H+0.67+ is bonded in a distorted single-bond geometry to one Mg2+ and one B3- atom. In the twenty-third H+0.67+ site, H+0.67+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the twenty-fourth H+0.67+ site, H+0.67+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Kinetic and modeling studies of the mechanism of the dehydrogenation of Mg(BH 4 ) 2 to Mg(B 3 H 8 ) 2

Since its discovery over 15 years ago, the reversible dehydrogenation of Mg(BH 4 ) 2 to Mg(B 3 H 8 ) 2 has remained one of the more intriguing hydrogen-cycling systems. While the mechanism of this reaction has been the subject of a good deal of speculation and computational studies, prior to this work it had not been probed through kinetic studies. Previous reports of the dehydrogenation of Mg(BH 4 ) 2 to Mg(B 3 H 8 ) 2 have not included kinetic studies. The present studies have shown that the dehydrogenation of Mg(BH 4 ) 2 to Mg(B 3 H 8 ) 2 is suppressed by hydrogen pressure indicating that the rate-limiting step in this process involves hydrogen elimination. Computational modeling of kinetic data obtained from monitoring the hydrogen elimination from Mg(BH 4 ) 2 to Mg(B 3 H 8 ) 2 under static vacuum over a range of temperatures supports that the dehydrogenation occurs through a reversible three-step process in which the elimination of hydrogen from the [B 3 H 10 ] − intermediate is rate limiting. A mechanism involving the low energy transfer of neighboring BH3 groups is proposed to account for the formation of [B 3 H 8 ] − at relatively low temperatures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗