Mg2Fe9O13 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded in a 6-coordinate geometry to two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms. There are five inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(6) and four equivalent O(7) atoms to form a mixture of corner and edge-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles are 8°. In the second Fe site, Fe(2) is bonded to one O(4), two equivalent O(1), and three equivalent O(3) atoms to form a mixture of corner and edge-sharing FeO6 octahedra. The corner-sharing octahedra are not tilted. In the third Fe site, Fe(3) is bonded to one O(5), two equivalent O(6), and three equivalent O(7) atoms to form a mixture of corner and edge-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles are 8°. In the fourth Fe site, Fe(4) is bonded in a 6-coordinate geometry to one O(1), one O(2), two equivalent O(3), and two equivalent O(4) atoms. In the fifth Fe site, Fe(5) is bonded in a 6-coordinate geometry to one O(2), one O(7), two equivalent O(5), and two equivalent O(6) atoms. There are seven inequivalent O sites. In the first O site, O(7) is bonded to one Fe(5), two equivalent Fe(1), and three equivalent Fe(3) atoms to form distorted OFe6 octahedra that share corners with two equivalent O(7)Fe6 octahedra, corners with two equivalent O(6)Fe5 square pyramids,  a cornercorner with one O(2)Mg2Fe2 tetrahedra,  a cornercorner with one O(5)Mg2Fe3 trigonal bipyramid, edges with five equivalent O(7)Fe6 octahedra, edges with five equivalent O(6)Fe5 square pyramids, and edges with two equivalent O(5)Mg2Fe3 trigonal bipyramids. The corner-sharing octahedra are not tilted. In the second O site, O(1) is bonded to two equivalent Fe(4) and four equivalent Fe(2) atoms to form OFe6 octahedra that share corners with four equivalent O(3)Fe5 square pyramids, corners with two equivalent O(2)Mg2Fe2 tetrahedra, edges with two equivalent O(1)Fe6 octahedra, edges with six equivalent O(3)Fe5 square pyramids, and edges with four equivalent O(4)Mg2Fe3 trigonal bipyramids. In the third O site, O(2) is bonded to two equivalent Mg(1), one Fe(4), and one Fe(5) atom to form OMg2Fe2 tetrahedra that share  a cornercorner with one O(1)Fe6 octahedra,  a cornercorner with one O(7)Fe6 octahedra, corners with two equivalent O(3)Fe5 square pyramids, corners with two equivalent O(6)Fe5 square pyramids, corners with two equivalent O(2)Mg2Fe2 tetrahedra, corners with four equivalent O(4)Mg2Fe3 trigonal bipyramids, corners with four equivalent O(5)Mg2Fe3 trigonal bipyramids,  an edgeedge with one O(4)Mg2Fe3 trigonal bipyramid, and  an edgeedge with one O(5)Mg2Fe3 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 7-10°. In the fourth O site, O(3) is bonded to two equivalent Fe(4) and three equivalent Fe(2) atoms to form OFe5 square pyramids that share corners with two equivalent O(1)Fe6 octahedra, corners with two equivalent O(2)Mg2Fe2 tetrahedra, corners with five equivalent O(4)Mg2Fe3 trigonal bipyramids, edges with three equivalent O(1)Fe6 octahedra, edges with four equivalent O(3)Fe5 square pyramids, and  an edgeedge with one O(4)Mg2Fe3 trigonal bipyramid. The corner-sharing octahedral tilt angles are 10°. In the fifth O site, O(4) is bonded to two equivalent Mg(1), one Fe(2), and two equivalent Fe(4) atoms to form distorted OMg2Fe3 trigonal bipyramids that share corners with five equivalent O(3)Fe5 square pyramids, corners with four equivalent O(2)Mg2Fe2 tetrahedra, corners with two equivalent O(5)Mg2Fe3 trigonal bipyramids, edges with two equivalent O(1)Fe6 octahedra,  an edgeedge with one O(3)Fe5 square pyramid,  an edgeedge with one O(2)Mg2Fe2 tetrahedra,  an edgeedge with one O(5)Mg2Fe3 trigonal bipyramid, and edges with two equivalent O(4)Mg2Fe3 trigonal bipyramids. In the sixth O site, O(5) is bonded to two equivalent Mg(1), one Fe(3), and two equivalent Fe(5) atoms to form distorted OMg2Fe3 trigonal bipyramids that share  a cornercorner with one O(7)Fe6 octahedra, corners with four equivalent O(6)Fe5 square pyramids, corners with four equivalent O(2)Mg2Fe2 tetrahedra, corners with two equivalent O(4)Mg2Fe3 trigonal bipyramids, edges with two equivalent O(7)Fe6 octahedra,  an edgeedge with one O(6)Fe5 square pyramid,  an edgeedge with one O(2)Mg2Fe2 tetrahedra,  an edgeedge with one O(4)Mg2Fe3 trigonal bipyramid, and edges with two equivalent O(5)Mg2Fe3 trigonal bipyramids. The corner-sharing octahedral tilt angles are 6°. In the seventh O site, O(6) is bonded to one Fe(1), two equivalent Fe(3), and two equivalent Fe(5) atoms to form OFe5 square pyramids that share corners with two equivalent O(7)Fe6 octahedra,  a cornercorner with one O(6)Fe5 square pyramid, corners with two equivalent O(2)Mg2Fe2 tetrahedra, corners with four equivalent O(5)Mg2Fe3 trigonal bipyramids, edges with five equivalent O(7)Fe6 octahedra, edges with two equivalent O(6)Fe5 square pyramids, and  an edgeedge with one O(5)Mg2Fe3 trigonal bipyramid. The corner-sharing octahedral tilt angles are 12°.
Mg2Fe9O13 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded in a 6-coordinate geometry to two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms. Both Mg(1)-O(2) bond lengths are 2.06 Å. Both Mg(1)-O(4) bond lengths are 2.29 Å. Both Mg(1)-O(5) bond lengths are 2.29 Å. There are five inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(6) and four equivalent O(7) atoms to form a mixture of corner and edge-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles are 8°. Both Fe(1)-O(6) bond lengths are 2.05 Å. All Fe(1)-O(7) bond lengths are 2.23 Å. In the second Fe site, Fe(2) is bonded to one O(4), two equivalent O(1), and three equivalent O(3) atoms to form a mixture of corner and edge-sharing FeO6 octahedra. The corner-sharing octahedra are not tilted. The Fe(2)-O(4) bond length is 1.93 Å. Both Fe(2)-O(1) bond lengths are 2.18 Å. There are two shorter (2.04 Å) and one longer (2.09 Å) Fe(2)-O(3) bond length. In the third Fe site, Fe(3) is bonded to one O(5), two equivalent O(6), and three equivalent O(7) atoms to form a mixture of corner and edge-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles are 8°. The Fe(3)-O(5) bond length is 1.94 Å. Both Fe(3)-O(6) bond lengths are 2.06 Å. There are two shorter (2.07 Å) and one longer (2.23 Å) Fe(3)-O(7) bond length. In the fourth Fe site, Fe(4) is bonded in a 6-coordinate geometry to one O(1), one O(2), two equivalent O(3), and two equivalent O(4) atoms. The Fe(4)-O(1) bond length is 2.44 Å. The Fe(4)-O(2) bond length is 1.97 Å. Both Fe(4)-O(3) bond lengths are 2.29 Å. Both Fe(4)-O(4) bond lengths are 2.16 Å. In the fifth Fe site, Fe(5) is bonded in a 6-coordinate geometry to one O(2), one O(7), two equivalent O(5), and two equivalent O(6) atoms. The Fe(5)-O(2) bond length is 1.97 Å. The Fe(5)-O(7) bond length is 2.62 Å. Both Fe(5)-O(5) bond lengths are 2.14 Å. Both Fe(5)-O(6) bond lengths are 2.29 Å. There are seven inequivalent O sites. In the first O site, O(7) is bonded to one Fe(5), two equivalent Fe(1), and three equivalent Fe(3) atoms to form distorted OFe6 octahedra that share corners with two equivalent O(7)Fe6 octahedra, corners with two equivalent O(6)Fe5 square pyramids,  a cornercorner with one O(2)Mg2Fe2 tetrahedra,  a cornercorner with one O(5)Mg2Fe3 trigonal bipyramid, edges with five equivalent O(7)Fe6 octahedra, edges with five equivalent O(6)Fe5 square pyramids, and edges with two equivalent O(5)Mg2Fe3 trigonal bipyramids. The corner-sharing octahedra are not tilted. In the second O site, O(1) is bonded to two equivalent Fe(4) and four equivalent Fe(2) atoms to form OFe6 octahedra that share corners with four equivalent O(3)Fe5 square pyramids, corners with two equivalent O(2)Mg2Fe2 tetrahedra, edges with two equivalent O(1)Fe6 octahedra, edges with six equivalent O(3)Fe5 square pyramids, and edges with four equivalent O(4)Mg2Fe3 trigonal bipyramids. In the third O site, O(2) is bonded to two equivalent Mg(1), one Fe(4), and one Fe(5) atom to form OMg2Fe2 tetrahedra that share  a cornercorner with one O(1)Fe6 octahedra,  a cornercorner with one O(7)Fe6 octahedra, corners with two equivalent O(3)Fe5 square pyramids, corners with two equivalent O(6)Fe5 square pyramids, corners with two equivalent O(2)Mg2Fe2 tetrahedra, corners with four equivalent O(4)Mg2Fe3 trigonal bipyramids, corners with four equivalent O(5)Mg2Fe3 trigonal bipyramids,  an edgeedge with one O(4)Mg2Fe3 trigonal bipyramid, and  an edgeedge with one O(5)Mg2Fe3 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 7-10°. In the fourth O site, O(3) is bonded to two equivalent Fe(4) and three equivalent Fe(2) atoms to form OFe5 square pyramids that share corners with two equivalent O(1)Fe6 octahedra, corners with two equivalent O(2)Mg2Fe2 tetrahedra, corners with five equivalent O(4)Mg2Fe3 trigonal bipyramids, edges with three equivalent O(1)Fe6 octahedra, edges with four equivalent O(3)Fe5 square pyramids, and  an edgeedge with one O(4)Mg2Fe3 trigonal bipyramid. The corner-sharing octahedral tilt angles are 10°. In the fifth O site, O(4) is bonded to two equivalent Mg(1), one Fe(2), and two equivalent Fe(4) atoms to form distorted OMg2Fe3 trigonal bipyramids that share corners with five equivalent O(3)Fe5 square pyramids, corners with four equivalent O(2)Mg2Fe2 tetrahedra, corners with two equivalent O(5)Mg2Fe3 trigonal bipyramids, edges with two equivalent O(1)Fe6 octahedra,  an edgeedge with one O(3)Fe5 square pyramid,  an edgeedge with one O(2)Mg2Fe2 tetrahedra,  an edgeedge with one O(5)Mg2Fe3 trigonal bipyramid, and edges with two equivalent O(4)Mg2Fe3 trigonal bipyramids. In the sixth O site, O(5) is bonded to two equivalent Mg(1), one Fe(3), and two equivalent Fe(5) atoms to form distorted OMg2Fe3 trigonal bipyramids that share  a cornercorner with one O(7)Fe6 octahedra, corners with four equivalent O(6)Fe5 square pyramids, corners with four equivalent O(2)Mg2Fe2 tetrahedra, corners with two equivalent O(4)Mg2Fe3 trigonal bipyramids, edges with two equivalent O(7)Fe6 octahedra,  an edgeedge with one O(6)Fe5 square pyramid,  an edgeedge with one O(2)Mg2Fe2 tetrahedra,  an edgeedge with one O(4)Mg2Fe3 trigonal bipyramid, and edges with two equivalent O(5)Mg2Fe3 trigonal bipyramids. The corner-sharing octahedral tilt angles are 6°. In the seventh O site, O(6) is bonded to one Fe(1), two equivalent Fe(3), and two equivalent Fe(5) atoms to form OFe5 square pyramids that share corners with two equivalent O(7)Fe6 octahedra,  a cornercorner with one O(6)Fe5 square pyramid, corners with two equivalent O(2)Mg2Fe2 tetrahedra, corners with four equivalent O(5)Mg2Fe3 trigonal bipyramids, edges with five equivalent O(7)Fe6 octahedra, edges with two equivalent O(6)Fe5 square pyramids, and  an edgeedge with one O(5)Mg2Fe3 trigonal bipyramid. The corner-sharing octahedral tilt angles are 12°.