Cr2AlO4 is Spinel structured and crystallizes in the trigonal R-3m space group. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form CrO6 octahedra that share corners with six equivalent Al(1)O4 tetrahedra, edges with two equivalent Cr(2)O6 octahedra, and edges with four equivalent Cr(1)O6 octahedra. In the second Cr site, Cr(2) is bonded to six equivalent O(1) atoms to form CrO6 octahedra that share corners with six equivalent Al(1)O4 tetrahedra and edges with six equivalent Cr(1)O6 octahedra. Al(1) is bonded to one O(2) and three equivalent O(1) atoms to form AlO4 tetrahedra that share corners with three equivalent Cr(2)O6 octahedra and corners with nine equivalent Cr(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 53-55°. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Cr(2), two equivalent Cr(1), and one Al(1) atom. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to three equivalent Cr(1) and one Al(1) atom.
Cr2AlO4 is Spinel structured and crystallizes in the trigonal R-3m space group. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form CrO6 octahedra that share corners with six equivalent Al(1)O4 tetrahedra, edges with two equivalent Cr(2)O6 octahedra, and edges with four equivalent Cr(1)O6 octahedra. Both Cr(1)-O(2) bond lengths are 2.15 Å. All Cr(1)-O(1) bond lengths are 2.10 Å. In the second Cr site, Cr(2) is bonded to six equivalent O(1) atoms to form CrO6 octahedra that share corners with six equivalent Al(1)O4 tetrahedra and edges with six equivalent Cr(1)O6 octahedra. All Cr(2)-O(1) bond lengths are 2.10 Å. Al(1) is bonded to one O(2) and three equivalent O(1) atoms to form AlO4 tetrahedra that share corners with three equivalent Cr(2)O6 octahedra and corners with nine equivalent Cr(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 53-55°. The Al(1)-O(2) bond length is 1.80 Å. All Al(1)-O(1) bond lengths are 1.85 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Cr(2), two equivalent Cr(1), and one Al(1) atom. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to three equivalent Cr(1) and one Al(1) atom.