Al5BO9 crystallizes in the orthorhombic Cmc2_1 space group. There are four inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(7) atom to form AlO6 octahedra that share corners with two equivalent Al(2)O4 tetrahedra,  a cornercorner with one Al(4)O5 trigonal bipyramid, edges with two equivalent Al(1)O6 octahedra, and  an edgeedge with one Al(4)O5 trigonal bipyramid. In the second Al site, Al(2) is bonded to one O(1), one O(6), and two equivalent O(7) atoms to form AlO4 tetrahedra that share corners with four equivalent Al(1)O6 octahedra, corners with two equivalent Al(4)O5 trigonal bipyramids, and  an edgeedge with one Al(4)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 49-56°. In the third Al site, Al(3) is bonded in a 5-coordinate geometry to one O(3), one O(4), one O(6), and two equivalent O(5) atoms. In the fourth Al site, Al(4) is bonded to one O(1), one O(4), one O(6), and two equivalent O(7) atoms to form distorted AlO5 trigonal bipyramids that share corners with two equivalent Al(1)O6 octahedra, corners with two equivalent Al(2)O4 tetrahedra, edges with two equivalent Al(1)O6 octahedra, and  an edgeedge with one Al(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 47°. B(1) is bonded in a trigonal planar geometry to one O(2) and two equivalent O(5) atoms. There are seven inequivalent O sites. In the first O site, O(6) is bonded in a T-shaped geometry to one Al(2), one Al(3), and one Al(4) atom. In the second O site, O(7) is bonded in a trigonal planar geometry to one Al(1), one Al(2), and one Al(4) atom. In the third O site, O(1) is bonded to one Al(2), one Al(4), and two equivalent Al(1) atoms to form corner-sharing OAl4 trigonal pyramids. In the fourth O site, O(2) is bonded in a distorted trigonal planar geometry to two equivalent Al(1) and one B(1) atom. In the fifth O site, O(3) is bonded in a trigonal planar geometry to one Al(3) and two equivalent Al(1) atoms. In the sixth O site, O(4) is bonded to one Al(3), one Al(4), and two equivalent Al(1) atoms to form corner-sharing OAl4 trigonal pyramids. In the seventh O site, O(5) is bonded in a trigonal planar geometry to one Al(1), one Al(3), and one B(1) atom.
Al5BO9 crystallizes in the orthorhombic Cmc2_1 space group. There are four inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(7) atom to form AlO6 octahedra that share corners with two equivalent Al(2)O4 tetrahedra,  a cornercorner with one Al(4)O5 trigonal bipyramid, edges with two equivalent Al(1)O6 octahedra, and  an edgeedge with one Al(4)O5 trigonal bipyramid. The Al(1)-O(1) bond length is 1.89 Å. The Al(1)-O(2) bond length is 1.91 Å. The Al(1)-O(3) bond length is 1.85 Å. The Al(1)-O(4) bond length is 1.91 Å. The Al(1)-O(5) bond length is 1.94 Å. The Al(1)-O(7) bond length is 1.90 Å. In the second Al site, Al(2) is bonded to one O(1), one O(6), and two equivalent O(7) atoms to form AlO4 tetrahedra that share corners with four equivalent Al(1)O6 octahedra, corners with two equivalent Al(4)O5 trigonal bipyramids, and  an edgeedge with one Al(4)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 49-56°. The Al(2)-O(1) bond length is 1.77 Å. The Al(2)-O(6) bond length is 1.77 Å. Both Al(2)-O(7) bond lengths are 1.73 Å. In the third Al site, Al(3) is bonded in a 5-coordinate geometry to one O(3), one O(4), one O(6), and two equivalent O(5) atoms. The Al(3)-O(3) bond length is 1.75 Å. The Al(3)-O(4) bond length is 2.20 Å. The Al(3)-O(6) bond length is 1.78 Å. Both Al(3)-O(5) bond lengths are 1.82 Å. In the fourth Al site, Al(4) is bonded to one O(1), one O(4), one O(6), and two equivalent O(7) atoms to form distorted AlO5 trigonal bipyramids that share corners with two equivalent Al(1)O6 octahedra, corners with two equivalent Al(2)O4 tetrahedra, edges with two equivalent Al(1)O6 octahedra, and  an edgeedge with one Al(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 47°. The Al(4)-O(1) bond length is 2.14 Å. The Al(4)-O(4) bond length is 1.81 Å. The Al(4)-O(6) bond length is 1.84 Å. Both Al(4)-O(7) bond lengths are 1.76 Å. B(1) is bonded in a trigonal planar geometry to one O(2) and two equivalent O(5) atoms. The B(1)-O(2) bond length is 1.36 Å. Both B(1)-O(5) bond lengths are 1.38 Å. There are seven inequivalent O sites. In the first O site, O(6) is bonded in a T-shaped geometry to one Al(2), one Al(3), and one Al(4) atom. In the second O site, O(7) is bonded in a trigonal planar geometry to one Al(1), one Al(2), and one Al(4) atom. In the third O site, O(1) is bonded to one Al(2), one Al(4), and two equivalent Al(1) atoms to form corner-sharing OAl4 trigonal pyramids. In the fourth O site, O(2) is bonded in a distorted trigonal planar geometry to two equivalent Al(1) and one B(1) atom. In the fifth O site, O(3) is bonded in a trigonal planar geometry to one Al(3) and two equivalent Al(1) atoms. In the sixth O site, O(4) is bonded to one Al(3), one Al(4), and two equivalent Al(1) atoms to form corner-sharing OAl4 trigonal pyramids. In the seventh O site, O(5) is bonded in a trigonal planar geometry to one Al(1), one Al(3), and one B(1) atom.