BaAl4O7 crystallizes in the orthorhombic Pnma space group. Ba(1) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(2), one O(4), and two equivalent O(3) atoms to form corner-sharing AlO4 tetrahedra. In the second Al site, Al(2) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form corner-sharing AlO4 tetrahedra. There are four inequivalent O sites. In the first O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Al(1), and one Al(2) atom. In the second O site, O(1) is bonded in a distorted bent 120 degrees geometry to two equivalent Ba(1) and two equivalent Al(2) atoms. In the third O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Al(1), and one Al(2) atom. In the fourth O site, O(3) is bonded in a trigonal planar geometry to one Al(2) and two equivalent Al(1) atoms.
BaAl4O7 crystallizes in the orthorhombic Pnma space group. Ba(1) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms. There is one shorter (3.01 Å) and one longer (3.03 Å) Ba(1)-O(1) bond length. Both Ba(1)-O(2) bond lengths are 2.87 Å. Both Ba(1)-O(4) bond lengths are 2.89 Å. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(2), one O(4), and two equivalent O(3) atoms to form corner-sharing AlO4 tetrahedra. The Al(1)-O(2) bond length is 1.75 Å. The Al(1)-O(4) bond length is 1.75 Å. Both Al(1)-O(3) bond lengths are 1.79 Å. In the second Al site, Al(2) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form corner-sharing AlO4 tetrahedra. The Al(2)-O(1) bond length is 1.76 Å. The Al(2)-O(2) bond length is 1.77 Å. The Al(2)-O(3) bond length is 1.82 Å. The Al(2)-O(4) bond length is 1.75 Å. There are four inequivalent O sites. In the first O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Al(1), and one Al(2) atom. In the second O site, O(1) is bonded in a distorted bent 120 degrees geometry to two equivalent Ba(1) and two equivalent Al(2) atoms. In the third O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Al(1), and one Al(2) atom. In the fourth O site, O(3) is bonded in a trigonal planar geometry to one Al(2) and two equivalent Al(1) atoms.