Mg(AlH4)2 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one H(1), one H(2), one H(3), one H(6), one H(7), and one H(8) atom to form MgH6 octahedra that share corners with three equivalent Al(1)H5 trigonal bipyramids and corners with three equivalent Al(2)H5 trigonal bipyramids. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one H(1), one H(2), one H(3), one H(4), and one H(5) atom to form distorted AlH5 trigonal bipyramids that share corners with three equivalent Mg(1)H6 octahedra and  an edgeedge with one Al(2)H5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 44-47°. In the second Al site, Al(2) is bonded to one H(4), one H(5), one H(6), one H(7), and one H(8) atom to form distorted AlH5 trigonal bipyramids that share corners with three equivalent Mg(1)H6 octahedra and  an edgeedge with one Al(1)H5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 45-48°. There are eight inequivalent H sites. In the first H site, H(1) is bonded in a bent 150 degrees geometry to one Mg(1) and one Al(1) atom. In the second H site, H(2) is bonded in a distorted bent 120 degrees geometry to one Mg(1) and one Al(1) atom. In the third H site, H(3) is bonded in a bent 120 degrees geometry to one Mg(1) and one Al(1) atom. In the fourth H site, H(4) is bonded in a water-like geometry to one Al(1) and one Al(2) atom. In the fifth H site, H(5) is bonded in a water-like geometry to one Al(1) and one Al(2) atom. In the sixth H site, H(6) is bonded in a bent 120 degrees geometry to one Mg(1) and one Al(2) atom. In the seventh H site, H(7) is bonded in a distorted bent 120 degrees geometry to one Mg(1) and one Al(2) atom. In the eighth H site, H(8) is bonded in a distorted bent 150 degrees geometry to one Mg(1) and one Al(2) atom.
Mg(AlH4)2 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one H(1), one H(2), one H(3), one H(6), one H(7), and one H(8) atom to form MgH6 octahedra that share corners with three equivalent Al(1)H5 trigonal bipyramids and corners with three equivalent Al(2)H5 trigonal bipyramids. The Mg(1)-H(1) bond length is 1.87 Å. The Mg(1)-H(2) bond length is 1.98 Å. The Mg(1)-H(3) bond length is 1.96 Å. The Mg(1)-H(6) bond length is 1.96 Å. The Mg(1)-H(7) bond length is 1.98 Å. The Mg(1)-H(8) bond length is 1.87 Å. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one H(1), one H(2), one H(3), one H(4), and one H(5) atom to form distorted AlH5 trigonal bipyramids that share corners with three equivalent Mg(1)H6 octahedra and  an edgeedge with one Al(2)H5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 44-47°. The Al(1)-H(1) bond length is 1.68 Å. The Al(1)-H(2) bond length is 1.64 Å. The Al(1)-H(3) bond length is 1.65 Å. The Al(1)-H(4) bond length is 2.05 Å. The Al(1)-H(5) bond length is 1.63 Å. In the second Al site, Al(2) is bonded to one H(4), one H(5), one H(6), one H(7), and one H(8) atom to form distorted AlH5 trigonal bipyramids that share corners with three equivalent Mg(1)H6 octahedra and  an edgeedge with one Al(1)H5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 45-48°. The Al(2)-H(4) bond length is 1.63 Å. The Al(2)-H(5) bond length is 2.04 Å. The Al(2)-H(6) bond length is 1.65 Å. The Al(2)-H(7) bond length is 1.64 Å. The Al(2)-H(8) bond length is 1.68 Å. There are eight inequivalent H sites. In the first H site, H(1) is bonded in a bent 150 degrees geometry to one Mg(1) and one Al(1) atom. In the second H site, H(2) is bonded in a distorted bent 120 degrees geometry to one Mg(1) and one Al(1) atom. In the third H site, H(3) is bonded in a bent 120 degrees geometry to one Mg(1) and one Al(1) atom. In the fourth H site, H(4) is bonded in a water-like geometry to one Al(1) and one Al(2) atom. In the fifth H site, H(5) is bonded in a water-like geometry to one Al(1) and one Al(2) atom. In the sixth H site, H(6) is bonded in a bent 120 degrees geometry to one Mg(1) and one Al(2) atom. In the seventh H site, H(7) is bonded in a distorted bent 120 degrees geometry to one Mg(1) and one Al(2) atom. In the eighth H site, H(8) is bonded in a distorted bent 150 degrees geometry to one Mg(1) and one Al(2) atom.