BaCr4AlO7 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 distorted BaO12 cuboctahedra that share corners with twelve equivalent Ba(1)O12 cuboctahedra, edges with nine equivalent Cr(1)O4 tetrahedra, edges with three equivalent Cr(2)O4 trigonal pyramids, and faces with four equivalent Al(1)O6 octahedra. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form CrO4 tetrahedra that share corners with three equivalent Al(1)O6 octahedra, corners with four equivalent Cr(1)O4 tetrahedra, corners with two equivalent Cr(2)O4 trigonal pyramids, and edges with three equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 44-51°. In the second Cr site, Cr(2) is bonded to one O(2) and three equivalent O(1) atoms to form CrO4 trigonal pyramids that share corners with three equivalent Al(1)O6 octahedra, corners with six equivalent Cr(1)O4 tetrahedra, and edges with three equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 48°. Al(1) is bonded to three equivalent O(1) and three equivalent O(3) atoms to form AlO6 octahedra that share corners with nine equivalent Cr(1)O4 tetrahedra, corners with three equivalent Cr(2)O4 trigonal pyramids, 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 3-coordinate geometry to two equivalent Ba(1), one Cr(1), one Cr(2), and one Al(1) atom. In the second O site, O(2) is bonded in a distorted tetrahedral geometry to one Cr(2) and three equivalent Cr(1) atoms. In the third O site, O(3) is bonded in a 3-coordinate geometry to two equivalent Ba(1), two equivalent Cr(1), and one Al(1) atom.
BaCr4AlO7 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 distorted BaO12 cuboctahedra that share corners with twelve equivalent Ba(1)O12 cuboctahedra, edges with nine equivalent Cr(1)O4 tetrahedra, edges with three equivalent Cr(2)O4 trigonal pyramids, and faces with four equivalent Al(1)O6 octahedra. All Ba(1)-O(1) bond lengths are 3.06 Å. There are three shorter (3.02 Å) and three longer (3.32 Å) Ba(1)-O(3) bond lengths. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form CrO4 tetrahedra that share corners with three equivalent Al(1)O6 octahedra, corners with four equivalent Cr(1)O4 tetrahedra, corners with two equivalent Cr(2)O4 trigonal pyramids, and edges with three equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 44-51°. The Cr(1)-O(1) bond length is 2.05 Å. The Cr(1)-O(2) bond length is 1.97 Å. Both Cr(1)-O(3) bond lengths are 2.03 Å. In the second Cr site, Cr(2) is bonded to one O(2) and three equivalent O(1) atoms to form CrO4 trigonal pyramids that share corners with three equivalent Al(1)O6 octahedra, corners with six equivalent Cr(1)O4 tetrahedra, and edges with three equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 48°. The Cr(2)-O(2) bond length is 1.90 Å. All Cr(2)-O(1) bond lengths are 1.99 Å. Al(1) is bonded to three equivalent O(1) and three equivalent O(3) atoms to form AlO6 octahedra that share corners with nine equivalent Cr(1)O4 tetrahedra, corners with three equivalent Cr(2)O4 trigonal pyramids, and faces with four equivalent Ba(1)O12 cuboctahedra. All Al(1)-O(1) bond lengths are 2.02 Å. All Al(1)-O(3) bond lengths are 1.97 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to two equivalent Ba(1), one Cr(1), one Cr(2), and one Al(1) atom. In the second O site, O(2) is bonded in a distorted tetrahedral geometry to one Cr(2) and three equivalent Cr(1) atoms. In the third O site, O(3) is bonded in a 3-coordinate geometry to two equivalent Ba(1), two equivalent Cr(1), and one Al(1) atom.