Mg(BH4)2 crystallizes in the orthorhombic F222 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to four equivalent H(2) and four equivalent H(4) atoms to form distorted MgH8 hexagonal bipyramids that share edges with four equivalent B(1)H4 tetrahedra. In the second Mg site, Mg(2) is bonded in a body-centered cubic geometry to four equivalent H(1) and four equivalent H(3) atoms. B(1) is bonded to one H(1), one H(2), one H(3), and one H(4) atom to form BH4 tetrahedra that share  an edgeedge with one Mg(1)H8 hexagonal bipyramid. There are four inequivalent H sites. In the first H site, H(3) is bonded in an L-shaped geometry to one Mg(2) and one B(1) atom. In the second H site, H(4) is bonded in an L-shaped geometry to one Mg(1) and one B(1) atom. In the third H site, H(1) is bonded in an L-shaped geometry to one Mg(2) and one B(1) atom. In the fourth H site, H(2) is bonded in an L-shaped geometry to one Mg(1) and one B(1) atom.
Mg(BH4)2 crystallizes in the orthorhombic F222 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to four equivalent H(2) and four equivalent H(4) atoms to form distorted MgH8 hexagonal bipyramids that share edges with four equivalent B(1)H4 tetrahedra. All Mg(1)-H(2) bond lengths are 2.01 Å. All Mg(1)-H(4) bond lengths are 2.05 Å. In the second Mg site, Mg(2) is bonded in a body-centered cubic geometry to four equivalent H(1) and four equivalent H(3) atoms. All Mg(2)-H(1) bond lengths are 2.04 Å. All Mg(2)-H(3) bond lengths are 2.06 Å. B(1) is bonded to one H(1), one H(2), one H(3), and one H(4) atom to form BH4 tetrahedra that share  an edgeedge with one Mg(1)H8 hexagonal bipyramid. The B(1)-H(1) bond length is 1.22 Å. The B(1)-H(2) bond length is 1.22 Å. The B(1)-H(3) bond length is 1.22 Å. The B(1)-H(4) bond length is 1.22 Å. There are four inequivalent H sites. In the first H site, H(3) is bonded in an L-shaped geometry to one Mg(2) and one B(1) atom. In the second H site, H(4) is bonded in an L-shaped geometry to one Mg(1) and one B(1) atom. In the third H site, H(1) is bonded in an L-shaped geometry to one Mg(2) and one B(1) atom. In the fourth H site, H(2) is bonded in an L-shaped geometry to one Mg(1) and one B(1) atom.