MgCr2O4 is Spinel-like structured and crystallizes in the monoclinic Cm space group. There are six inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(13), one O(3), and two equivalent O(1) atoms to form MgO4 tetrahedra that share  a cornercorner with one Mg(6)O6 octahedra, corners with two equivalent Mg(3)O6 octahedra, corners with two equivalent Cr(6)O6 octahedra, corners with three equivalent Cr(3)O6 octahedra, and corners with four equivalent Cr(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 56-61°. In the second Mg site, Mg(2) is bonded to one O(5), one O(9), two equivalent O(4), and two equivalent O(7) atoms to form MgO6 octahedra that share corners with three equivalent Cr(2)O4 tetrahedra, corners with three equivalent Cr(7)O4 tetrahedra,  an edgeedge with one Mg(3)O6 octahedra,  an edgeedge with one Mg(5)O6 octahedra, edges with two equivalent Cr(1)O6 octahedra, and edges with two equivalent Cr(4)O6 octahedra. In the third Mg site, Mg(3) is bonded to one O(2), one O(8), two equivalent O(1), and two equivalent O(7) atoms to form MgO6 octahedra that share  a cornercorner with one Cr(2)O4 tetrahedra,  a cornercorner with one Cr(9)O4 tetrahedra, corners with two equivalent Mg(1)O4 tetrahedra, corners with two equivalent Cr(7)O4 tetrahedra,  an edgeedge with one Mg(2)O6 octahedra,  an edgeedge with one Cr(3)O6 octahedra, and edges with four equivalent Cr(1)O6 octahedra. In the fourth Mg site, Mg(4) is bonded to one O(11), one O(15), two equivalent O(10), and two equivalent O(12) atoms to form MgO6 octahedra that share corners with three equivalent Cr(5)O4 tetrahedra, corners with three equivalent Cr(8)O4 tetrahedra,  an edgeedge with one Mg(5)O6 octahedra,  an edgeedge with one Mg(6)O6 octahedra, edges with two equivalent Cr(4)O6 octahedra, and edges with two equivalent Cr(6)O6 octahedra. In the fifth Mg site, Mg(5) is bonded to one O(14), one O(6), two equivalent O(12), and two equivalent O(4) atoms to form MgO6 octahedra that share  a cornercorner with one Cr(5)O4 tetrahedra,  a cornercorner with one Cr(7)O4 tetrahedra, corners with two equivalent Cr(2)O4 tetrahedra, corners with two equivalent Cr(8)O4 tetrahedra,  an edgeedge with one Mg(2)O6 octahedra,  an edgeedge with one Mg(4)O6 octahedra, and edges with four equivalent Cr(4)O6 octahedra. In the sixth Mg site, Mg(6) is bonded to one O(13), one O(18), two equivalent O(10), and two equivalent O(17) atoms to form MgO6 octahedra that share  a cornercorner with one Mg(1)O4 tetrahedra,  a cornercorner with one Cr(8)O4 tetrahedra, corners with two equivalent Cr(5)O4 tetrahedra, corners with two equivalent Cr(9)O4 tetrahedra,  an edgeedge with one Mg(4)O6 octahedra,  an edgeedge with one Cr(3)O6 octahedra, and edges with four equivalent Cr(6)O6 octahedra. There are nine inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(1), one O(2), one O(3), one O(5), one O(7), and one O(8) atom to form CrO6 octahedra that share  a cornercorner with one Cr(2)O4 tetrahedra,  a cornercorner with one Cr(9)O4 tetrahedra, corners with two equivalent Mg(1)O4 tetrahedra, corners with two equivalent Cr(7)O4 tetrahedra,  an edgeedge with one Mg(2)O6 octahedra,  an edgeedge with one Cr(3)O6 octahedra, edges with two equivalent Mg(3)O6 octahedra, and edges with two equivalent Cr(1)O6 octahedra. In the second Cr site, Cr(2) is bonded to one O(2), one O(9), and two equivalent O(4) atoms to form CrO4 tetrahedra that share  a cornercorner with one Mg(3)O6 octahedra, corners with two equivalent Mg(5)O6 octahedra, corners with two equivalent Cr(1)O6 octahedra, corners with three equivalent Mg(2)O6 octahedra, and corners with four equivalent Cr(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 53-65°. In the third Cr site, Cr(3) is bonded to one O(16), one O(3), two equivalent O(1), and two equivalent O(17) atoms to form CrO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, corners with three equivalent Cr(9)O4 tetrahedra,  an edgeedge with one Mg(3)O6 octahedra,  an edgeedge with one Mg(6)O6 octahedra, edges with two equivalent Cr(1)O6 octahedra, and edges with two equivalent Cr(6)O6 octahedra. In the fourth Cr site, Cr(4) is bonded to one O(11), one O(12), one O(14), one O(4), one O(6), and one O(9) atom to form CrO6 octahedra that share  a cornercorner with one Cr(5)O4 tetrahedra,  a cornercorner with one Cr(7)O4 tetrahedra, corners with two equivalent Cr(2)O4 tetrahedra, corners with two equivalent Cr(8)O4 tetrahedra,  an edgeedge with one Mg(2)O6 octahedra,  an edgeedge with one Mg(4)O6 octahedra, edges with two equivalent Mg(5)O6 octahedra, and edges with two equivalent Cr(4)O6 octahedra. In the fifth Cr site, Cr(5) is bonded to one O(15), one O(6), and two equivalent O(10) atoms to form CrO4 tetrahedra that share  a cornercorner with one Mg(5)O6 octahedra, corners with two equivalent Mg(6)O6 octahedra, corners with two equivalent Cr(4)O6 octahedra, corners with three equivalent Mg(4)O6 octahedra, and corners with four equivalent Cr(6)O6 octahedra. The corner-sharing octahedral tilt angles range from 53-66°. In the sixth Cr site, Cr(6) is bonded to one O(10), one O(13), one O(15), one O(16), one O(17), and one O(18) atom to form CrO6 octahedra that share  a cornercorner with one Mg(1)O4 tetrahedra,  a cornercorner with one Cr(8)O4 tetrahedra, corners with two equivalent Cr(5)O4 tetrahedra, corners with two equivalent Cr(9)O4 tetrahedra,  an edgeedge with one Mg(4)O6 octahedra,  an edgeedge with one Cr(3)O6 octahedra, edges with two equivalent Mg(6)O6 octahedra, and edges with two equivalent Cr(6)O6 octahedra. In the seventh Cr site, Cr(7) is bonded to one O(14), one O(5), and two equivalent O(7) atoms to form CrO4 tetrahedra that share  a cornercorner with one Mg(5)O6 octahedra, corners with two equivalent Mg(3)O6 octahedra, corners with two equivalent Cr(4)O6 octahedra, corners with three equivalent Mg(2)O6 octahedra, and corners with four equivalent Cr(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 54-64°. In the eighth Cr site, Cr(8) is bonded to one O(11), one O(18), and two equivalent O(12) atoms to form CrO4 tetrahedra that share  a cornercorner with one Mg(6)O6 octahedra, corners with two equivalent Mg(5)O6 octahedra, corners with two equivalent Cr(6)O6 octahedra, corners with three equivalent Mg(4)O6 octahedra, and corners with four equivalent Cr(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 54-65°. In the ninth Cr site, Cr(9) is bonded to one O(16), one O(8), and two equivalent O(17) atoms to form CrO4 tetrahedra that share  a cornercorner with one Mg(3)O6 octahedra, corners with two equivalent Mg(6)O6 octahedra, corners with two equivalent Cr(1)O6 octahedra, corners with three equivalent Cr(3)O6 octahedra, and corners with four equivalent Cr(6)O6 octahedra. The corner-sharing octahedral tilt angles range from 55-63°. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Mg(3), one Cr(1), and one Cr(3) atom. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Mg(3), one Cr(2), and two equivalent Cr(1) atoms. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Cr(3), and two equivalent Cr(1) atoms. In the fourth O site, O(4) is bonded in a rectangular see-saw-like geometry to one Mg(2), one Mg(5), one Cr(2), and one Cr(4) atom. In the fifth O site, O(5) is bonded in a rectangular see-saw-like geometry to one Mg(2), one Cr(7), and two equivalent Cr(1) atoms. In the sixth O site, O(6) is bonded in a rectangular see-saw-like geometry to one Mg(5), one Cr(5), and two equivalent Cr(4) atoms. In the seventh O site, O(7) is bonded in a rectangular see-saw-like geometry to one Mg(2), one Mg(3), one Cr(1), and one Cr(7) atom. In the eighth O site, O(8) is bonded in a rectangular see-saw-like geometry to one Mg(3), one Cr(9), and two equivalent Cr(1) atoms. In the ninth O site, O(9) is bonded in a rectangular see-saw-like geometry to one Mg(2), one Cr(2), and two equivalent Cr(4) atoms. In the tenth O site, O(10) is bonded in a rectangular see-saw-like geometry to one Mg(4), one Mg(6), one Cr(5), and one Cr(6) atom. In the eleventh O site, O(11) is bonded in a rectangular see-saw-like geometry to one Mg(4), one Cr(8), and two equivalent Cr(4) atoms. In the twelfth O site, O(12) is bonded in a rectangular see-saw-like geometry to one Mg(4), one Mg(5), one Cr(4), and one Cr(8) atom. In the thirteenth O site, O(13) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Mg(6), and two equivalent Cr(6) atoms. In the fourteenth O site, O(14) is bonded in a rectangular see-saw-like geometry to one Mg(5), one Cr(7), and two equivalent Cr(4) atoms. In the fifteenth O site, O(15) is bonded in a rectangular see-saw-like geometry to one Mg(4), one Cr(5), and two equivalent Cr(6) atoms. In the sixteenth O site, O(16) is bonded in a rectangular see-saw-like geometry to one Cr(3), one Cr(9), and two equivalent Cr(6) atoms. In the seventeenth O site, O(17) is bonded in a rectangular see-saw-like geometry to one Mg(6), one Cr(3), one Cr(6), and one Cr(9) atom. In the eighteenth O site, O(18) is bonded in a rectangular see-saw-like geometry to one Mg(6), one Cr(8), and two equivalent Cr(6) atoms.
MgCr2O4 is Spinel-like structured and crystallizes in the monoclinic Cm space group. There are six inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(13), one O(3), and two equivalent O(1) atoms to form MgO4 tetrahedra that share  a cornercorner with one Mg(6)O6 octahedra, corners with two equivalent Mg(3)O6 octahedra, corners with two equivalent Cr(6)O6 octahedra, corners with three equivalent Cr(3)O6 octahedra, and corners with four equivalent Cr(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 56-61°. The Mg(1)-O(13) bond length is 2.01 Å. The Mg(1)-O(3) bond length is 2.03 Å. Both Mg(1)-O(1) bond lengths are 1.97 Å. In the second Mg site, Mg(2) is bonded to one O(5), one O(9), two equivalent O(4), and two equivalent O(7) atoms to form MgO6 octahedra that share corners with three equivalent Cr(2)O4 tetrahedra, corners with three equivalent Cr(7)O4 tetrahedra,  an edgeedge with one Mg(3)O6 octahedra,  an edgeedge with one Mg(5)O6 octahedra, edges with two equivalent Cr(1)O6 octahedra, and edges with two equivalent Cr(4)O6 octahedra. The Mg(2)-O(5) bond length is 2.10 Å. The Mg(2)-O(9) bond length is 2.11 Å. Both Mg(2)-O(4) bond lengths are 2.09 Å. Both Mg(2)-O(7) bond lengths are 2.10 Å. In the third Mg site, Mg(3) is bonded to one O(2), one O(8), two equivalent O(1), and two equivalent O(7) atoms to form MgO6 octahedra that share  a cornercorner with one Cr(2)O4 tetrahedra,  a cornercorner with one Cr(9)O4 tetrahedra, corners with two equivalent Mg(1)O4 tetrahedra, corners with two equivalent Cr(7)O4 tetrahedra,  an edgeedge with one Mg(2)O6 octahedra,  an edgeedge with one Cr(3)O6 octahedra, and edges with four equivalent Cr(1)O6 octahedra. The Mg(3)-O(2) bond length is 2.12 Å. The Mg(3)-O(8) bond length is 2.10 Å. Both Mg(3)-O(1) bond lengths are 2.06 Å. Both Mg(3)-O(7) bond lengths are 2.08 Å. In the fourth Mg site, Mg(4) is bonded to one O(11), one O(15), two equivalent O(10), and two equivalent O(12) atoms to form MgO6 octahedra that share corners with three equivalent Cr(5)O4 tetrahedra, corners with three equivalent Cr(8)O4 tetrahedra,  an edgeedge with one Mg(5)O6 octahedra,  an edgeedge with one Mg(6)O6 octahedra, edges with two equivalent Cr(4)O6 octahedra, and edges with two equivalent Cr(6)O6 octahedra. The Mg(4)-O(11) bond length is 2.11 Å. The Mg(4)-O(15) bond length is 2.10 Å. Both Mg(4)-O(10) bond lengths are 2.10 Å. Both Mg(4)-O(12) bond lengths are 2.09 Å. In the fifth Mg site, Mg(5) is bonded to one O(14), one O(6), two equivalent O(12), and two equivalent O(4) atoms to form MgO6 octahedra that share  a cornercorner with one Cr(5)O4 tetrahedra,  a cornercorner with one Cr(7)O4 tetrahedra, corners with two equivalent Cr(2)O4 tetrahedra, corners with two equivalent Cr(8)O4 tetrahedra,  an edgeedge with one Mg(2)O6 octahedra,  an edgeedge with one Mg(4)O6 octahedra, and edges with four equivalent Cr(4)O6 octahedra. The Mg(5)-O(14) bond length is 2.09 Å. The Mg(5)-O(6) bond length is 2.10 Å. Both Mg(5)-O(12) bond lengths are 2.10 Å. Both Mg(5)-O(4) bond lengths are 2.09 Å. In the sixth Mg site, Mg(6) is bonded to one O(13), one O(18), two equivalent O(10), and two equivalent O(17) atoms to form MgO6 octahedra that share  a cornercorner with one Mg(1)O4 tetrahedra,  a cornercorner with one Cr(8)O4 tetrahedra, corners with two equivalent Cr(5)O4 tetrahedra, corners with two equivalent Cr(9)O4 tetrahedra,  an edgeedge with one Mg(4)O6 octahedra,  an edgeedge with one Cr(3)O6 octahedra, and edges with four equivalent Cr(6)O6 octahedra. The Mg(6)-O(13) bond length is 2.03 Å. The Mg(6)-O(18) bond length is 2.08 Å. Both Mg(6)-O(10) bond lengths are 2.10 Å. Both Mg(6)-O(17) bond lengths are 2.12 Å. There are nine inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(1), one O(2), one O(3), one O(5), one O(7), and one O(8) atom to form CrO6 octahedra that share  a cornercorner with one Cr(2)O4 tetrahedra,  a cornercorner with one Cr(9)O4 tetrahedra, corners with two equivalent Mg(1)O4 tetrahedra, corners with two equivalent Cr(7)O4 tetrahedra,  an edgeedge with one Mg(2)O6 octahedra,  an edgeedge with one Cr(3)O6 octahedra, edges with two equivalent Mg(3)O6 octahedra, and edges with two equivalent Cr(1)O6 octahedra. The Cr(1)-O(1) bond length is 1.99 Å. The Cr(1)-O(2) bond length is 2.03 Å. The Cr(1)-O(3) bond length is 2.03 Å. The Cr(1)-O(5) bond length is 2.03 Å. The Cr(1)-O(7) bond length is 2.03 Å. The Cr(1)-O(8) bond length is 2.04 Å. In the second Cr site, Cr(2) is bonded to one O(2), one O(9), and two equivalent O(4) atoms to form CrO4 tetrahedra that share  a cornercorner with one Mg(3)O6 octahedra, corners with two equivalent Mg(5)O6 octahedra, corners with two equivalent Cr(1)O6 octahedra, corners with three equivalent Mg(2)O6 octahedra, and corners with four equivalent Cr(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 53-65°. The Cr(2)-O(2) bond length is 1.97 Å. The Cr(2)-O(9) bond length is 1.99 Å. Both Cr(2)-O(4) bond lengths are 1.91 Å. In the third Cr site, Cr(3) is bonded to one O(16), one O(3), two equivalent O(1), and two equivalent O(17) atoms to form CrO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, corners with three equivalent Cr(9)O4 tetrahedra,  an edgeedge with one Mg(3)O6 octahedra,  an edgeedge with one Mg(6)O6 octahedra, edges with two equivalent Cr(1)O6 octahedra, and edges with two equivalent Cr(6)O6 octahedra. The Cr(3)-O(16) bond length is 2.05 Å. The Cr(3)-O(3) bond length is 2.00 Å. Both Cr(3)-O(1) bond lengths are 1.98 Å. Both Cr(3)-O(17) bond lengths are 2.05 Å. In the fourth Cr site, Cr(4) is bonded to one O(11), one O(12), one O(14), one O(4), one O(6), and one O(9) atom to form CrO6 octahedra that share  a cornercorner with one Cr(5)O4 tetrahedra,  a cornercorner with one Cr(7)O4 tetrahedra, corners with two equivalent Cr(2)O4 tetrahedra, corners with two equivalent Cr(8)O4 tetrahedra,  an edgeedge with one Mg(2)O6 octahedra,  an edgeedge with one Mg(4)O6 octahedra, edges with two equivalent Mg(5)O6 octahedra, and edges with two equivalent Cr(4)O6 octahedra. The Cr(4)-O(11) bond length is 2.04 Å. The Cr(4)-O(12) bond length is 2.03 Å. The Cr(4)-O(14) bond length is 2.03 Å. The Cr(4)-O(4) bond length is 2.02 Å. The Cr(4)-O(6) bond length is 2.03 Å. The Cr(4)-O(9) bond length is 2.03 Å. In the fifth Cr site, Cr(5) is bonded to one O(15), one O(6), and two equivalent O(10) atoms to form CrO4 tetrahedra that share  a cornercorner with one Mg(5)O6 octahedra, corners with two equivalent Mg(6)O6 octahedra, corners with two equivalent Cr(4)O6 octahedra, corners with three equivalent Mg(4)O6 octahedra, and corners with four equivalent Cr(6)O6 octahedra. The corner-sharing octahedral tilt angles range from 53-66°. The Cr(5)-O(15) bond length is 2.00 Å. The Cr(5)-O(6) bond length is 1.97 Å. Both Cr(5)-O(10) bond lengths are 1.90 Å. In the sixth Cr site, Cr(6) is bonded to one O(10), one O(13), one O(15), one O(16), one O(17), and one O(18) atom to form CrO6 octahedra that share  a cornercorner with one Mg(1)O4 tetrahedra,  a cornercorner with one Cr(8)O4 tetrahedra, corners with two equivalent Cr(5)O4 tetrahedra, corners with two equivalent Cr(9)O4 tetrahedra,  an edgeedge with one Mg(4)O6 octahedra,  an edgeedge with one Cr(3)O6 octahedra, edges with two equivalent Mg(6)O6 octahedra, and edges with two equivalent Cr(6)O6 octahedra. The Cr(6)-O(10) bond length is 2.02 Å. The Cr(6)-O(13) bond length is 2.01 Å. The Cr(6)-O(15) bond length is 2.03 Å. The Cr(6)-O(16) bond length is 2.04 Å. The Cr(6)-O(17) bond length is 2.03 Å. The Cr(6)-O(18) bond length is 2.04 Å. In the seventh Cr site, Cr(7) is bonded to one O(14), one O(5), and two equivalent O(7) atoms to form CrO4 tetrahedra that share  a cornercorner with one Mg(5)O6 octahedra, corners with two equivalent Mg(3)O6 octahedra, corners with two equivalent Cr(4)O6 octahedra, corners with three equivalent Mg(2)O6 octahedra, and corners with four equivalent Cr(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 54-64°. The Cr(7)-O(14) bond length is 1.99 Å. The Cr(7)-O(5) bond length is 1.99 Å. Both Cr(7)-O(7) bond lengths are 1.90 Å. In the eighth Cr site, Cr(8) is bonded to one O(11), one O(18), and two equivalent O(12) atoms to form CrO4 tetrahedra that share  a cornercorner with one Mg(6)O6 octahedra, corners with two equivalent Mg(5)O6 octahedra, corners with two equivalent Cr(6)O6 octahedra, corners with three equivalent Mg(4)O6 octahedra, and corners with four equivalent Cr(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 54-65°. The Cr(8)-O(11) bond length is 1.98 Å. The Cr(8)-O(18) bond length is 2.00 Å. Both Cr(8)-O(12) bond lengths are 1.91 Å. In the ninth Cr site, Cr(9) is bonded to one O(16), one O(8), and two equivalent O(17) atoms to form CrO4 tetrahedra that share  a cornercorner with one Mg(3)O6 octahedra, corners with two equivalent Mg(6)O6 octahedra, corners with two equivalent Cr(1)O6 octahedra, corners with three equivalent Cr(3)O6 octahedra, and corners with four equivalent Cr(6)O6 octahedra. The corner-sharing octahedral tilt angles range from 55-63°. The Cr(9)-O(16) bond length is 2.04 Å. The Cr(9)-O(8) bond length is 1.94 Å. Both Cr(9)-O(17) bond lengths are 1.93 Å. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Mg(3), one Cr(1), and one Cr(3) atom. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Mg(3), one Cr(2), and two equivalent Cr(1) atoms. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Cr(3), and two equivalent Cr(1) atoms. In the fourth O site, O(4) is bonded in a rectangular see-saw-like geometry to one Mg(2), one Mg(5), one Cr(2), and one Cr(4) atom. In the fifth O site, O(5) is bonded in a rectangular see-saw-like geometry to one Mg(2), one Cr(7), and two equivalent Cr(1) atoms. In the sixth O site, O(6) is bonded in a rectangular see-saw-like geometry to one Mg(5), one Cr(5), and two equivalent Cr(4) atoms. In the seventh O site, O(7) is bonded in a rectangular see-saw-like geometry to one Mg(2), one Mg(3), one Cr(1), and one Cr(7) atom. In the eighth O site, O(8) is bonded in a rectangular see-saw-like geometry to one Mg(3), one Cr(9), and two equivalent Cr(1) atoms. In the ninth O site, O(9) is bonded in a rectangular see-saw-like geometry to one Mg(2), one Cr(2), and two equivalent Cr(4) atoms. In the tenth O site, O(10) is bonded in a rectangular see-saw-like geometry to one Mg(4), one Mg(6), one Cr(5), and one Cr(6) atom. In the eleventh O site, O(11) is bonded in a rectangular see-saw-like geometry to one Mg(4), one Cr(8), and two equivalent Cr(4) atoms. In the twelfth O site, O(12) is bonded in a rectangular see-saw-like geometry to one Mg(4), one Mg(5), one Cr(4), and one Cr(8) atom. In the thirteenth O site, O(13) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Mg(6), and two equivalent Cr(6) atoms. In the fourteenth O site, O(14) is bonded in a rectangular see-saw-like geometry to one Mg(5), one Cr(7), and two equivalent Cr(4) atoms. In the fifteenth O site, O(15) is bonded in a rectangular see-saw-like geometry to one Mg(4), one Cr(5), and two equivalent Cr(6) atoms. In the sixteenth O site, O(16) is bonded in a rectangular see-saw-like geometry to one Cr(3), one Cr(9), and two equivalent Cr(6) atoms. In the seventeenth O site, O(17) is bonded in a rectangular see-saw-like geometry to one Mg(6), one Cr(3), one Cr(6), and one Cr(9) atom. In the eighteenth O site, O(18) is bonded in a rectangular see-saw-like geometry to one Mg(6), one Cr(8), and two equivalent Cr(6) atoms.