Ba2Cu3AlO8 crystallizes in the tetragonal P4/mmm space group. Ba(1) is bonded in a 12-coordinate geometry to four equivalent O(1), four equivalent O(2), and four equivalent O(3) atoms. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(3) and four equivalent O(1) atoms to form distorted CuO5 trigonal bipyramids that share  a cornercorner with one Cu(2)O6 octahedra and corners with four equivalent Cu(1)O5 trigonal bipyramids. The corner-sharing octahedra are not tilted. In the second Cu site, Cu(2) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form CuO6 octahedra that share corners with four equivalent Cu(2)O6 octahedra and corners with two equivalent Cu(1)O5 trigonal bipyramids. The corner-sharing octahedra are not tilted. Al(1) is bonded in a body-centered cubic geometry to eight equivalent O(1) atoms. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to two equivalent Ba(1), two equivalent Cu(1), and two equivalent Al(1) atoms. In the second O site, O(2) is bonded in a distorted linear geometry to four equivalent Ba(1) and two equivalent Cu(2) atoms. In the third O site, O(3) is bonded to four equivalent Ba(1), one Cu(1), and one Cu(2) atom to form a mixture of corner and edge-sharing OBa4Cu2 octahedra. The corner-sharing octahedral tilt angles range from 0-6°.
Ba2Cu3AlO8 crystallizes in the tetragonal P4/mmm space group. Ba(1) is bonded in a 12-coordinate geometry to four equivalent O(1), four equivalent O(2), and four equivalent O(3) atoms. All Ba(1)-O(1) bond lengths are 3.24 Å. All Ba(1)-O(2) bond lengths are 2.75 Å. All Ba(1)-O(3) bond lengths are 2.70 Å. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(3) and four equivalent O(1) atoms to form distorted CuO5 trigonal bipyramids that share  a cornercorner with one Cu(2)O6 octahedra and corners with four equivalent Cu(1)O5 trigonal bipyramids. The corner-sharing octahedra are not tilted. The Cu(1)-O(3) bond length is 2.00 Å. All Cu(1)-O(1) bond lengths are 1.97 Å. In the second Cu site, Cu(2) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form CuO6 octahedra that share corners with four equivalent Cu(2)O6 octahedra and corners with two equivalent Cu(1)O5 trigonal bipyramids. The corner-sharing octahedra are not tilted. Both Cu(2)-O(3) bond lengths are 2.12 Å. All Cu(2)-O(2) bond lengths are 1.91 Å. Al(1) is bonded in a body-centered cubic geometry to eight equivalent O(1) atoms. All Al(1)-O(1) bond lengths are 2.24 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to two equivalent Ba(1), two equivalent Cu(1), and two equivalent Al(1) atoms. In the second O site, O(2) is bonded in a distorted linear geometry to four equivalent Ba(1) and two equivalent Cu(2) atoms. In the third O site, O(3) is bonded to four equivalent Ba(1), one Cu(1), and one Cu(2) atom to form a mixture of corner and edge-sharing OBa4Cu2 octahedra. The corner-sharing octahedral tilt angles range from 0-6°.