KAl(BH4)4 crystallizes in the orthorhombic Fddd space group. K(1) is bonded in a 8-coordinate geometry to four equivalent H(2) and four equivalent H(4) atoms. Al(1) is bonded to four equivalent H(1) and four equivalent H(3) atoms to form distorted AlH8 hexagonal bipyramids that share edges with four equivalent B(1)H4 tetrahedra. 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 Al(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 Al(1) and one B(1) atom. In the second H site, H(4) is bonded in a single-bond geometry to one K(1) and one B(1) atom. In the third H site, H(1) is bonded in an L-shaped geometry to one Al(1) and one B(1) atom. In the fourth H site, H(2) is bonded in a distorted single-bond geometry to one K(1) and one B(1) atom.
KAl(BH4)4 crystallizes in the orthorhombic Fddd space group. K(1) is bonded in a 8-coordinate geometry to four equivalent H(2) and four equivalent H(4) atoms. All K(1)-H(2) bond lengths are 2.81 Å. All K(1)-H(4) bond lengths are 2.91 Å. Al(1) is bonded to four equivalent H(1) and four equivalent H(3) atoms to form distorted AlH8 hexagonal bipyramids that share edges with four equivalent B(1)H4 tetrahedra. All Al(1)-H(1) bond lengths are 1.85 Å. All Al(1)-H(3) bond lengths are 1.88 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 Al(1)H8 hexagonal bipyramid. The B(1)-H(1) bond length is 1.25 Å. The B(1)-H(2) bond length is 1.21 Å. The B(1)-H(3) bond length is 1.24 Å. The B(1)-H(4) bond length is 1.21 Å. There are four inequivalent H sites. In the first H site, H(3) is bonded in an L-shaped geometry to one Al(1) and one B(1) atom. In the second H site, H(4) is bonded in a single-bond geometry to one K(1) and one B(1) atom. In the third H site, H(1) is bonded in an L-shaped geometry to one Al(1) and one B(1) atom. In the fourth H site, H(2) is bonded in a distorted single-bond geometry to one K(1) and one B(1) atom.