BaCu4AlO7 crystallizes in the hexagonal P6_3mc space group. Ba(1) is bonded to six equivalent O(1) and six equivalent O(3) atoms to form BaO12 cuboctahedra that share corners with twelve equivalent Ba(1)O12 cuboctahedra, edges with three equivalent Cu(2)O4 tetrahedra, edges with nine equivalent Cu(1)O4 tetrahedra, and faces with four equivalent Al(1)O6 octahedra. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form CuO4 tetrahedra that share corners with three equivalent Al(1)O6 octahedra, corners with two equivalent Cu(2)O4 tetrahedra, corners with four equivalent Cu(1)O4 tetrahedra, and edges with three equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 47-54°. In the second Cu site, Cu(2) is bonded to one O(2) and three equivalent O(1) atoms to form CuO4 tetrahedra that share corners with three equivalent Al(1)O6 octahedra, corners with six equivalent Cu(1)O4 tetrahedra, and edges with three equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 51°. Al(1) is bonded to three equivalent O(1) and three equivalent O(3) atoms to form AlO6 octahedra that share corners with three equivalent Cu(2)O4 tetrahedra, corners with nine equivalent Cu(1)O4 tetrahedra, and faces with four equivalent Ba(1)O12 cuboctahedra. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to two equivalent Ba(1), one Cu(1), one Cu(2), and one Al(1) atom. In the second O site, O(2) is bonded in a tetrahedral geometry to one Cu(2) and three equivalent Cu(1) atoms. In the third O site, O(3) is bonded in a 3-coordinate geometry to two equivalent Ba(1), two equivalent Cu(1), and one Al(1) atom.
BaCu4AlO7 crystallizes in the hexagonal P6_3mc space group. Ba(1) is bonded to six equivalent O(1) and six equivalent O(3) atoms to form BaO12 cuboctahedra that share corners with twelve equivalent Ba(1)O12 cuboctahedra, edges with three equivalent Cu(2)O4 tetrahedra, edges with nine equivalent Cu(1)O4 tetrahedra, and faces with four equivalent Al(1)O6 octahedra. All Ba(1)-O(1) bond lengths are 3.00 Å. There are three shorter (2.99 Å) and three longer (3.07 Å) Ba(1)-O(3) bond lengths. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form CuO4 tetrahedra that share corners with three equivalent Al(1)O6 octahedra, corners with two equivalent Cu(2)O4 tetrahedra, corners with four equivalent Cu(1)O4 tetrahedra, and edges with three equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 47-54°. The Cu(1)-O(1) bond length is 1.95 Å. The Cu(1)-O(2) bond length is 1.92 Å. Both Cu(1)-O(3) bond lengths are 1.93 Å. In the second Cu site, Cu(2) is bonded to one O(2) and three equivalent O(1) atoms to form CuO4 tetrahedra that share corners with three equivalent Al(1)O6 octahedra, corners with six equivalent Cu(1)O4 tetrahedra, and edges with three equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 51°. The Cu(2)-O(2) bond length is 1.92 Å. All Cu(2)-O(1) bond lengths are 1.94 Å. Al(1) is bonded to three equivalent O(1) and three equivalent O(3) atoms to form AlO6 octahedra that share corners with three equivalent Cu(2)O4 tetrahedra, corners with nine equivalent Cu(1)O4 tetrahedra, and faces with four equivalent Ba(1)O12 cuboctahedra. All Al(1)-O(1) bond lengths are 1.95 Å. All Al(1)-O(3) bond lengths are 1.93 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to two equivalent Ba(1), one Cu(1), one Cu(2), and one Al(1) atom. In the second O site, O(2) is bonded in a tetrahedral geometry to one Cu(2) and three equivalent Cu(1) atoms. In the third O site, O(3) is bonded in a 3-coordinate geometry to two equivalent Ba(1), two equivalent Cu(1), and one Al(1) atom.