MgCr2O4 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to one O(1), two equivalent O(3), and two equivalent O(4) atoms to form MgO5 square pyramids that share corners with two equivalent Cr(1)O6 octahedra, corners with four equivalent Cr(2)O6 octahedra, edges with three equivalent Cr(1)O6 octahedra, edges with two equivalent Mg(1)O5 square pyramids, and  a faceface with one Cr(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 7-59°. 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 CrO6 octahedra that share corners with four equivalent Cr(2)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, edges with four equivalent Cr(1)O6 octahedra, and edges with three equivalent Mg(1)O5 square pyramids. The corner-sharing octahedral tilt angles range from 49-56°. In the second Cr site, Cr(2) is bonded to one O(1), two equivalent O(2), and three equivalent O(4) atoms to form CrO6 octahedra that share corners with four equivalent Cr(1)O6 octahedra, corners with four equivalent Mg(1)O5 square pyramids, edges with four equivalent Cr(2)O6 octahedra, and  a faceface with one Mg(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 49-56°. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Cr(2), and two equivalent Cr(1) atoms to form OMgCr3 trigonal pyramids that share corners with two equivalent O(3)Mg2Cr3 square pyramids,  a cornercorner with one O(4)Mg2Cr3 trigonal bipyramid, corners with two equivalent O(1)MgCr3 trigonal pyramids, edges with three equivalent O(3)Mg2Cr3 square pyramids, and edges with two equivalent O(4)Mg2Cr3 trigonal bipyramids. In the second O site, O(2) is bonded in a trigonal planar geometry to one Cr(1) and two equivalent Cr(2) atoms. In the third O site, O(3) is bonded to two equivalent Mg(1) and three equivalent Cr(1) atoms to form OMg2Cr3 square pyramids that share corners with two equivalent O(4)Mg2Cr3 trigonal bipyramids, corners with two equivalent O(1)MgCr3 trigonal pyramids, edges with four equivalent O(3)Mg2Cr3 square pyramids,  an edgeedge with one O(4)Mg2Cr3 trigonal bipyramid, and edges with three equivalent O(1)MgCr3 trigonal pyramids. In the fourth O site, O(4) is bonded to two equivalent Mg(1) and three equivalent Cr(2) atoms to form distorted OMg2Cr3 trigonal bipyramids that share corners with two equivalent O(3)Mg2Cr3 square pyramids,  a cornercorner with one O(1)MgCr3 trigonal pyramid,  an edgeedge with one O(3)Mg2Cr3 square pyramid, edges with four equivalent O(4)Mg2Cr3 trigonal bipyramids, and edges with two equivalent O(1)MgCr3 trigonal pyramids.
MgCr2O4 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to one O(1), two equivalent O(3), and two equivalent O(4) atoms to form MgO5 square pyramids that share corners with two equivalent Cr(1)O6 octahedra, corners with four equivalent Cr(2)O6 octahedra, edges with three equivalent Cr(1)O6 octahedra, edges with two equivalent Mg(1)O5 square pyramids, and  a faceface with one Cr(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 7-59°. The Mg(1)-O(1) bond length is 2.06 Å. Both Mg(1)-O(3) bond lengths are 2.06 Å. Both Mg(1)-O(4) bond lengths are 2.08 Å. 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 CrO6 octahedra that share corners with four equivalent Cr(2)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, edges with four equivalent Cr(1)O6 octahedra, and edges with three equivalent Mg(1)O5 square pyramids. The corner-sharing octahedral tilt angles range from 49-56°. The Cr(1)-O(2) bond length is 1.95 Å. Both Cr(1)-O(1) bond lengths are 1.96 Å. There are two shorter (2.11 Å) and one longer (2.21 Å) Cr(1)-O(3) bond length. In the second Cr site, Cr(2) is bonded to one O(1), two equivalent O(2), and three equivalent O(4) atoms to form CrO6 octahedra that share corners with four equivalent Cr(1)O6 octahedra, corners with four equivalent Mg(1)O5 square pyramids, edges with four equivalent Cr(2)O6 octahedra, and  a faceface with one Mg(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 49-56°. The Cr(2)-O(1) bond length is 2.03 Å. Both Cr(2)-O(2) bond lengths are 1.95 Å. There is one shorter (2.02 Å) and two longer (2.17 Å) Cr(2)-O(4) bond lengths. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Cr(2), and two equivalent Cr(1) atoms to form OMgCr3 trigonal pyramids that share corners with two equivalent O(3)Mg2Cr3 square pyramids,  a cornercorner with one O(4)Mg2Cr3 trigonal bipyramid, corners with two equivalent O(1)MgCr3 trigonal pyramids, edges with three equivalent O(3)Mg2Cr3 square pyramids, and edges with two equivalent O(4)Mg2Cr3 trigonal bipyramids. In the second O site, O(2) is bonded in a trigonal planar geometry to one Cr(1) and two equivalent Cr(2) atoms. In the third O site, O(3) is bonded to two equivalent Mg(1) and three equivalent Cr(1) atoms to form OMg2Cr3 square pyramids that share corners with two equivalent O(4)Mg2Cr3 trigonal bipyramids, corners with two equivalent O(1)MgCr3 trigonal pyramids, edges with four equivalent O(3)Mg2Cr3 square pyramids,  an edgeedge with one O(4)Mg2Cr3 trigonal bipyramid, and edges with three equivalent O(1)MgCr3 trigonal pyramids. In the fourth O site, O(4) is bonded to two equivalent Mg(1) and three equivalent Cr(2) atoms to form distorted OMg2Cr3 trigonal bipyramids that share corners with two equivalent O(3)Mg2Cr3 square pyramids,  a cornercorner with one O(1)MgCr3 trigonal pyramid,  an edgeedge with one O(3)Mg2Cr3 square pyramid, edges with four equivalent O(4)Mg2Cr3 trigonal bipyramids, and edges with two equivalent O(1)MgCr3 trigonal pyramids.