MgCr4O8 crystallizes in the monoclinic P2 space group. Mg(1) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form MgO6 octahedra that share corners with four equivalent Cr(1)O6 octahedra, edges with two equivalent Cr(2)O6 octahedra, edges with two equivalent Cr(4)O6 octahedra, and faces with two equivalent Cr(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 41-51°. There are four inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form CrO6 octahedra that share corners with four equivalent Mg(1)O6 octahedra, corners with four equivalent Cr(2)O6 octahedra, corners with four equivalent Cr(4)O6 octahedra, and edges with two equivalent Cr(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 41-53°. In the second Cr site, Cr(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form CrO6 octahedra that share corners with four equivalent Cr(1)O6 octahedra, corners with four equivalent Cr(3)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, and edges with two equivalent Cr(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-53°. In the third Cr site, Cr(3) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form CrO6 octahedra that share corners with four equivalent Cr(2)O6 octahedra, corners with four equivalent Cr(4)O6 octahedra, edges with two equivalent Cr(1)O6 octahedra, and faces with two equivalent Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-50°. In the fourth Cr site, Cr(4) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form CrO6 octahedra that share corners with four equivalent Cr(1)O6 octahedra, corners with four equivalent Cr(3)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, and edges with two equivalent Cr(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-50°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Cr(1), one Cr(2), and one Cr(4) atom. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Cr(1), one Cr(2), and one Cr(3) atom. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Cr(2), one Cr(3), and one Cr(4) atom. In the fourth O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Cr(1), one Cr(3), and one Cr(4) atom.
MgCr4O8 crystallizes in the monoclinic P2 space group. Mg(1) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form MgO6 octahedra that share corners with four equivalent Cr(1)O6 octahedra, edges with two equivalent Cr(2)O6 octahedra, edges with two equivalent Cr(4)O6 octahedra, and faces with two equivalent Cr(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 41-51°. Both Mg(1)-O(2) bond lengths are 1.97 Å. Both Mg(1)-O(3) bond lengths are 2.02 Å. Both Mg(1)-O(4) bond lengths are 2.06 Å. There are four inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form CrO6 octahedra that share corners with four equivalent Mg(1)O6 octahedra, corners with four equivalent Cr(2)O6 octahedra, corners with four equivalent Cr(4)O6 octahedra, and edges with two equivalent Cr(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 41-53°. Both Cr(1)-O(1) bond lengths are 2.06 Å. Both Cr(1)-O(2) bond lengths are 2.01 Å. Both Cr(1)-O(4) bond lengths are 2.09 Å. In the second Cr site, Cr(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form CrO6 octahedra that share corners with four equivalent Cr(1)O6 octahedra, corners with four equivalent Cr(3)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, and edges with two equivalent Cr(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-53°. Both Cr(2)-O(1) bond lengths are 1.98 Å. Both Cr(2)-O(2) bond lengths are 2.06 Å. Both Cr(2)-O(3) bond lengths are 1.97 Å. In the third Cr site, Cr(3) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form CrO6 octahedra that share corners with four equivalent Cr(2)O6 octahedra, corners with four equivalent Cr(4)O6 octahedra, edges with two equivalent Cr(1)O6 octahedra, and faces with two equivalent Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-50°. Both Cr(3)-O(2) bond lengths are 2.02 Å. Both Cr(3)-O(3) bond lengths are 2.02 Å. Both Cr(3)-O(4) bond lengths are 2.01 Å. In the fourth Cr site, Cr(4) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form CrO6 octahedra that share corners with four equivalent Cr(1)O6 octahedra, corners with four equivalent Cr(3)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, and edges with two equivalent Cr(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-50°. Both Cr(4)-O(1) bond lengths are 1.94 Å. Both Cr(4)-O(3) bond lengths are 1.98 Å. Both Cr(4)-O(4) bond lengths are 2.01 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Cr(1), one Cr(2), and one Cr(4) atom. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Cr(1), one Cr(2), and one Cr(3) atom. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Cr(2), one Cr(3), and one Cr(4) atom. In the fourth O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Cr(1), one Cr(3), and one Cr(4) atom.