MgCr4O8 crystallizes in the trigonal R-3m space group. Mg(1) is bonded to six equivalent O(1) atoms to form MgO6 octahedra that share corners with six equivalent Cr(1)O6 octahedra and edges with six equivalent Cr(2)O6 octahedra. The corner-sharing octahedral tilt angles are 10°. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to six equivalent O(1) atoms to form CrO6 octahedra that share corners with six equivalent Mg(1)O6 octahedra and edges with six equivalent Cr(2)O6 octahedra. The corner-sharing octahedral tilt angles are 10°. In the second Cr site, Cr(2) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form CrO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Cr(1)O6 octahedra, and edges with four equivalent Cr(2)O6 octahedra. There are two inequivalent O sites. In the first O site, O(1) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Cr(1), and two equivalent Cr(2) atoms. In the second O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to three equivalent Cr(2) atoms.
MgCr4O8 crystallizes in the trigonal R-3m space group. Mg(1) is bonded to six equivalent O(1) atoms to form MgO6 octahedra that share corners with six equivalent Cr(1)O6 octahedra and edges with six equivalent Cr(2)O6 octahedra. The corner-sharing octahedral tilt angles are 10°. All Mg(1)-O(1) bond lengths are 2.15 Å. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to six equivalent O(1) atoms to form CrO6 octahedra that share corners with six equivalent Mg(1)O6 octahedra and edges with six equivalent Cr(2)O6 octahedra. The corner-sharing octahedral tilt angles are 10°. All Cr(1)-O(1) bond lengths are 2.06 Å. In the second Cr site, Cr(2) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form CrO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Cr(1)O6 octahedra, and edges with four equivalent Cr(2)O6 octahedra. Both Cr(2)-O(2) bond lengths are 1.95 Å. All Cr(2)-O(1) bond lengths are 1.98 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Cr(1), and two equivalent Cr(2) atoms. In the second O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to three equivalent Cr(2) atoms.