MgCr2(FeO4)2 crystallizes in the monoclinic Pm space group. Mg(1) is bonded to one O(1), one O(5), and two equivalent O(4) atoms to form MgO4 tetrahedra that share corners with six equivalent Fe(1)O6 octahedra, corners with two equivalent Cr(2)O4 tetrahedra, and  an edgeedge with one Cr(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 63-66°. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(1), one O(5), and two equivalent O(3) atoms to form CrO4 tetrahedra that share corners with six equivalent Fe(1)O6 octahedra and  an edgeedge with one Mg(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 49-59°. In the second Cr site, Cr(2) is bonded to one O(2), one O(6), and two equivalent O(4) atoms to form CrO4 tetrahedra that share corners with six equivalent Fe(1)O6 octahedra and corners with two equivalent Mg(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 47-55°. Fe(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form FeO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, corners with three equivalent Cr(1)O4 tetrahedra, corners with three equivalent Cr(2)O4 tetrahedra, and edges with two equivalent Fe(1)O6 octahedra. There are six inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Cr(1), and two equivalent Fe(1) atoms to form distorted edge-sharing OMgCrFe2 tetrahedra. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Cr(2) and two equivalent Fe(1) atoms. In the third O site, O(3) is bonded in a bent 120 degrees geometry to one Cr(1) and one Fe(1) atom. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Mg(1), one Cr(2), and one Fe(1) atom. In the fifth O site, O(5) is bonded to one Mg(1), one Cr(1), and two equivalent Fe(1) atoms to form distorted edge-sharing OMgCrFe2 tetrahedra. In the sixth O site, O(6) is bonded in a trigonal planar geometry to one Cr(2) and two equivalent Fe(1) atoms.
MgCr2(FeO4)2 crystallizes in the monoclinic Pm space group. Mg(1) is bonded to one O(1), one O(5), and two equivalent O(4) atoms to form MgO4 tetrahedra that share corners with six equivalent Fe(1)O6 octahedra, corners with two equivalent Cr(2)O4 tetrahedra, and  an edgeedge with one Cr(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 63-66°. The Mg(1)-O(1) bond length is 2.07 Å. The Mg(1)-O(5) bond length is 2.06 Å. Both Mg(1)-O(4) bond lengths are 1.95 Å. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(1), one O(5), and two equivalent O(3) atoms to form CrO4 tetrahedra that share corners with six equivalent Fe(1)O6 octahedra and  an edgeedge with one Mg(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 49-59°. The Cr(1)-O(1) bond length is 1.92 Å. The Cr(1)-O(5) bond length is 1.90 Å. Both Cr(1)-O(3) bond lengths are 1.72 Å. In the second Cr site, Cr(2) is bonded to one O(2), one O(6), and two equivalent O(4) atoms to form CrO4 tetrahedra that share corners with six equivalent Fe(1)O6 octahedra and corners with two equivalent Mg(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 47-55°. The Cr(2)-O(2) bond length is 1.80 Å. The Cr(2)-O(6) bond length is 1.82 Å. Both Cr(2)-O(4) bond lengths are 1.81 Å. Fe(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form FeO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, corners with three equivalent Cr(1)O4 tetrahedra, corners with three equivalent Cr(2)O4 tetrahedra, and edges with two equivalent Fe(1)O6 octahedra. The Fe(1)-O(1) bond length is 2.06 Å. The Fe(1)-O(2) bond length is 2.02 Å. The Fe(1)-O(3) bond length is 1.88 Å. The Fe(1)-O(4) bond length is 1.92 Å. The Fe(1)-O(5) bond length is 2.09 Å. The Fe(1)-O(6) bond length is 1.98 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Cr(1), and two equivalent Fe(1) atoms to form distorted edge-sharing OMgCrFe2 tetrahedra. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Cr(2) and two equivalent Fe(1) atoms. In the third O site, O(3) is bonded in a bent 120 degrees geometry to one Cr(1) and one Fe(1) atom. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Mg(1), one Cr(2), and one Fe(1) atom. In the fifth O site, O(5) is bonded to one Mg(1), one Cr(1), and two equivalent Fe(1) atoms to form distorted edge-sharing OMgCrFe2 tetrahedra. In the sixth O site, O(6) is bonded in a trigonal planar geometry to one Cr(2) and two equivalent Fe(1) atoms.