Cr2O3 crystallizes in the orthorhombic Cmcm space group. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(2), two equivalent O(1), and three equivalent O(3) atoms to form a mixture of corner and edge-sharing CrO6 octahedra. The corner-sharing octahedra are not tilted. In the second Cr site, Cr(2) is bonded in a 6-coordinate geometry to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Cr(2) and four equivalent Cr(1) atoms to form OCr6 octahedra that share corners with four equivalent O(3)Cr5 square pyramids, edges with two equivalent O(1)Cr6 octahedra, and edges with six equivalent O(3)Cr5 square pyramids. In the second O site, O(2) is bonded in a trigonal non-coplanar geometry to one Cr(1) and two equivalent Cr(2) atoms. In the third O site, O(3) is bonded to two equivalent Cr(2) and three equivalent Cr(1) atoms to form OCr5 square pyramids that share corners with two equivalent O(1)Cr6 octahedra, edges with three equivalent O(1)Cr6 octahedra, and edges with four equivalent O(3)Cr5 square pyramids. The corner-sharing octahedral tilt angles are 7°. In the fourth O site, O(4) is bonded in a bent 120 degrees geometry to two equivalent Cr(2) atoms.
Cr2O3 crystallizes in the orthorhombic Cmcm space group. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(2), two equivalent O(1), and three equivalent O(3) atoms to form a mixture of corner and edge-sharing CrO6 octahedra. The corner-sharing octahedra are not tilted. The Cr(1)-O(2) bond length is 1.93 Å. Both Cr(1)-O(1) bond lengths are 2.12 Å. There are two shorter (2.04 Å) and one longer (2.09 Å) Cr(1)-O(3) bond length. In the second Cr site, Cr(2) is bonded in a 6-coordinate geometry to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms. The Cr(2)-O(1) bond length is 2.44 Å. The Cr(2)-O(4) bond length is 1.82 Å. Both Cr(2)-O(2) bond lengths are 1.93 Å. Both Cr(2)-O(3) bond lengths are 2.33 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Cr(2) and four equivalent Cr(1) atoms to form OCr6 octahedra that share corners with four equivalent O(3)Cr5 square pyramids, edges with two equivalent O(1)Cr6 octahedra, and edges with six equivalent O(3)Cr5 square pyramids. In the second O site, O(2) is bonded in a trigonal non-coplanar geometry to one Cr(1) and two equivalent Cr(2) atoms. In the third O site, O(3) is bonded to two equivalent Cr(2) and three equivalent Cr(1) atoms to form OCr5 square pyramids that share corners with two equivalent O(1)Cr6 octahedra, edges with three equivalent O(1)Cr6 octahedra, and edges with four equivalent O(3)Cr5 square pyramids. The corner-sharing octahedral tilt angles are 7°. In the fourth O site, O(4) is bonded in a bent 120 degrees geometry to two equivalent Cr(2) atoms.