DOE OSTI2020
Mg(AlH4)2 crystallizes in the triclinic P1 space group. The structure is three-dimensional. Mg2+ is bonded to six H1- atoms to form MgH6 octahedra that share corners with six AlH5 trigonal bipyramids. There are a spread of Mg–H bond distances ranging from 1.87–1.98 Å. There are two inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to five H1- atoms to form distorted AlH5 trigonal bipyramids that share corners with three equivalent MgH6 octahedra and an edgeedge with one AlH5 trigonal bipyramid. The corner-sharing octahedra tilt angles range from 44–47°. There are a spread of Al–H bond distances ranging from 1.63–2.05 Å. In the second Al3+ site, Al3+ is bonded to five H1- atoms to form distorted AlH5 trigonal bipyramids that share corners with three equivalent MgH6 octahedra and an edgeedge with one AlH5 trigonal bipyramid. The corner-sharing octahedra tilt angles range from 45–48°. There are a spread of Al–H bond distances ranging from 1.63–2.04 Å. There are eight inequivalent H1- sites. In the first H1- site, H1- is bonded in a bent 150 degrees geometry to one Mg2+ and one Al3+ atom. In the second H1- site, H1- is bonded in a distorted bent 120 degrees geometry to one Mg2+ and one Al3+ atom. In the third H1- site, H1- is bonded in a bent 120 degrees geometry to one Mg2+ and one Al3+ atom. In the fourth H1- site, H1- is bonded in a water-like geometry to two Al3+ atoms. In the fifth H1- site, H1- is bonded in a water-like geometry to two Al3+ atoms. In the sixth H1- site, H1- is bonded in a bent 120 degrees geometry to one Mg2+ and one Al3+ atom. In the seventh H1- site, H1- is bonded in a distorted bent 120 degrees geometry to one Mg2+ and one Al3+ atom. In the eighth H1- site, H1- is bonded in a distorted bent 150 degrees geometry to one Mg2+ and one Al3+ atom.