MgCr2Al4O10 crystallizes in the orthorhombic Amm2 space group. Mg(1) is bonded in a 7-coordinate geometry to one O(4), two equivalent O(2), and four equivalent O(1) atoms. There are two 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 two equivalent Cr(1)O6 octahedra, corners with two equivalent Al(2)O6 octahedra, corners with two equivalent Al(1)O5 trigonal bipyramids, and edges with four equivalent Al(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 21-25°. In the second Cr site, Cr(2) is bonded in a 6-coordinate geometry to two equivalent O(3), two equivalent O(5), and two equivalent O(6) atoms. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(3), one O(6), and two equivalent O(5) atoms to form AlO5 trigonal bipyramids that share  a cornercorner with one Cr(1)O6 octahedra, corners with two equivalent Al(2)O6 octahedra, corners with three equivalent Al(1)O5 trigonal bipyramids, and  an edgeedge with one Al(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 71-72°. In the second Al site, Al(2) is bonded to one O(1), one O(4), one O(5), one O(6), and two equivalent O(2) atoms to form distorted AlO6 octahedra that share  a cornercorner with one Cr(1)O6 octahedra, corners with three equivalent Al(2)O6 octahedra, corners with two equivalent Al(1)O5 trigonal bipyramids, edges with two equivalent Cr(1)O6 octahedra, and  an edgeedge with one Al(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 21-57°. There are six inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Mg(1), one Cr(1), one Al(1), and one Al(2) atom to form OMg2Al2Cr trigonal bipyramids that share  a cornercorner with one O(3)Al2Cr2 tetrahedra,  a cornercorner with one O(4)MgAl2Cr2 trigonal bipyramid, corners with four equivalent O(1)Mg2Al2Cr trigonal bipyramids, corners with three equivalent O(5)Al3Cr trigonal pyramids, corners with four equivalent O(2)MgAl2Cr trigonal pyramids, edges with two equivalent O(4)MgAl2Cr2 trigonal bipyramids, edges with two equivalent O(2)MgAl2Cr trigonal pyramids, and  a faceface with one O(1)Mg2Al2Cr trigonal bipyramid. In the second O site, O(2) is bonded to one Mg(1), one Cr(1), and two equivalent Al(2) atoms to form OMgAl2Cr trigonal pyramids that share  a cornercorner with one O(4)MgAl2Cr2 trigonal bipyramid, corners with four equivalent O(1)Mg2Al2Cr trigonal bipyramids, corners with two equivalent O(5)Al3Cr trigonal pyramids, corners with two equivalent O(2)MgAl2Cr trigonal pyramids, edges with two equivalent O(1)Mg2Al2Cr trigonal bipyramids, edges with two equivalent O(4)MgAl2Cr2 trigonal bipyramids, and  an edgeedge with one O(2)MgAl2Cr trigonal pyramid. In the third O site, O(3) is bonded to two equivalent Cr(2) and two equivalent Al(1) atoms to form distorted OAl2Cr2 tetrahedra that share corners with two equivalent O(3)Al2Cr2 tetrahedra, corners with two equivalent O(1)Mg2Al2Cr trigonal bipyramids, and edges with four equivalent O(5)Al3Cr trigonal pyramids. In the fourth O site, O(4) is bonded to one Mg(1), two equivalent Cr(1), and two equivalent Al(2) atoms to form distorted OMgAl2Cr2 trigonal bipyramids that share corners with two equivalent O(1)Mg2Al2Cr trigonal bipyramids, corners with two equivalent O(4)MgAl2Cr2 trigonal bipyramids, corners with two equivalent O(5)Al3Cr trigonal pyramids, corners with two equivalent O(2)MgAl2Cr trigonal pyramids, edges with four equivalent O(1)Mg2Al2Cr trigonal bipyramids, and edges with four equivalent O(2)MgAl2Cr trigonal pyramids. In the fifth O site, O(5) is bonded to one Cr(2), one Al(2), and two equivalent Al(1) atoms to form OAl3Cr trigonal pyramids that share  a cornercorner with one O(4)MgAl2Cr2 trigonal bipyramid, corners with three equivalent O(1)Mg2Al2Cr trigonal bipyramids, corners with two equivalent O(2)MgAl2Cr trigonal pyramids, corners with three equivalent O(5)Al3Cr trigonal pyramids, and edges with two equivalent O(3)Al2Cr2 tetrahedra. In the sixth O site, O(6) is bonded in a distorted T-shaped geometry to one Cr(2), one Al(1), and one Al(2) atom.
MgCr2Al4O10 crystallizes in the orthorhombic Amm2 space group. Mg(1) is bonded in a 7-coordinate geometry to one O(4), two equivalent O(2), and four equivalent O(1) atoms. The Mg(1)-O(4) bond length is 2.37 Å. Both Mg(1)-O(2) bond lengths are 2.15 Å. All Mg(1)-O(1) bond lengths are 2.29 Å. There are two 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 two equivalent Cr(1)O6 octahedra, corners with two equivalent Al(2)O6 octahedra, corners with two equivalent Al(1)O5 trigonal bipyramids, and edges with four equivalent Al(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 21-25°. Both Cr(1)-O(1) bond lengths are 1.99 Å. Both Cr(1)-O(2) bond lengths are 2.00 Å. Both Cr(1)-O(4) bond lengths are 1.89 Å. In the second Cr site, Cr(2) is bonded in a 6-coordinate geometry to two equivalent O(3), two equivalent O(5), and two equivalent O(6) atoms. Both Cr(2)-O(3) bond lengths are 2.02 Å. Both Cr(2)-O(5) bond lengths are 2.15 Å. Both Cr(2)-O(6) bond lengths are 1.93 Å. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(3), one O(6), and two equivalent O(5) atoms to form AlO5 trigonal bipyramids that share  a cornercorner with one Cr(1)O6 octahedra, corners with two equivalent Al(2)O6 octahedra, corners with three equivalent Al(1)O5 trigonal bipyramids, and  an edgeedge with one Al(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 71-72°. The Al(1)-O(1) bond length is 1.94 Å. The Al(1)-O(3) bond length is 1.96 Å. The Al(1)-O(6) bond length is 1.77 Å. Both Al(1)-O(5) bond lengths are 1.97 Å. In the second Al site, Al(2) is bonded to one O(1), one O(4), one O(5), one O(6), and two equivalent O(2) atoms to form distorted AlO6 octahedra that share  a cornercorner with one Cr(1)O6 octahedra, corners with three equivalent Al(2)O6 octahedra, corners with two equivalent Al(1)O5 trigonal bipyramids, edges with two equivalent Cr(1)O6 octahedra, and  an edgeedge with one Al(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 21-57°. The Al(2)-O(1) bond length is 2.00 Å. The Al(2)-O(4) bond length is 2.17 Å. The Al(2)-O(5) bond length is 1.95 Å. The Al(2)-O(6) bond length is 1.80 Å. Both Al(2)-O(2) bond lengths are 1.90 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Mg(1), one Cr(1), one Al(1), and one Al(2) atom to form OMg2Al2Cr trigonal bipyramids that share  a cornercorner with one O(3)Al2Cr2 tetrahedra,  a cornercorner with one O(4)MgAl2Cr2 trigonal bipyramid, corners with four equivalent O(1)Mg2Al2Cr trigonal bipyramids, corners with three equivalent O(5)Al3Cr trigonal pyramids, corners with four equivalent O(2)MgAl2Cr trigonal pyramids, edges with two equivalent O(4)MgAl2Cr2 trigonal bipyramids, edges with two equivalent O(2)MgAl2Cr trigonal pyramids, and  a faceface with one O(1)Mg2Al2Cr trigonal bipyramid. In the second O site, O(2) is bonded to one Mg(1), one Cr(1), and two equivalent Al(2) atoms to form OMgAl2Cr trigonal pyramids that share  a cornercorner with one O(4)MgAl2Cr2 trigonal bipyramid, corners with four equivalent O(1)Mg2Al2Cr trigonal bipyramids, corners with two equivalent O(5)Al3Cr trigonal pyramids, corners with two equivalent O(2)MgAl2Cr trigonal pyramids, edges with two equivalent O(1)Mg2Al2Cr trigonal bipyramids, edges with two equivalent O(4)MgAl2Cr2 trigonal bipyramids, and  an edgeedge with one O(2)MgAl2Cr trigonal pyramid. In the third O site, O(3) is bonded to two equivalent Cr(2) and two equivalent Al(1) atoms to form distorted OAl2Cr2 tetrahedra that share corners with two equivalent O(3)Al2Cr2 tetrahedra, corners with two equivalent O(1)Mg2Al2Cr trigonal bipyramids, and edges with four equivalent O(5)Al3Cr trigonal pyramids. In the fourth O site, O(4) is bonded to one Mg(1), two equivalent Cr(1), and two equivalent Al(2) atoms to form distorted OMgAl2Cr2 trigonal bipyramids that share corners with two equivalent O(1)Mg2Al2Cr trigonal bipyramids, corners with two equivalent O(4)MgAl2Cr2 trigonal bipyramids, corners with two equivalent O(5)Al3Cr trigonal pyramids, corners with two equivalent O(2)MgAl2Cr trigonal pyramids, edges with four equivalent O(1)Mg2Al2Cr trigonal bipyramids, and edges with four equivalent O(2)MgAl2Cr trigonal pyramids. In the fifth O site, O(5) is bonded to one Cr(2), one Al(2), and two equivalent Al(1) atoms to form OAl3Cr trigonal pyramids that share  a cornercorner with one O(4)MgAl2Cr2 trigonal bipyramid, corners with three equivalent O(1)Mg2Al2Cr trigonal bipyramids, corners with two equivalent O(2)MgAl2Cr trigonal pyramids, corners with three equivalent O(5)Al3Cr trigonal pyramids, and edges with two equivalent O(3)Al2Cr2 tetrahedra. In the sixth O site, O(6) is bonded in a distorted T-shaped geometry to one Cr(2), one Al(1), and one Al(2) atom.