Mg(Fe5O8)2 is beta indium sulfide-derived structured and crystallizes in the trigonal R3m space group. Mg(1) is bonded to one O(6) and three equivalent O(1) atoms to form MgO4 tetrahedra that share corners with three equivalent Fe(1)O6 octahedra, corners with three equivalent Fe(5)O6 octahedra, and corners with six equivalent Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 55-60°. There are six inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to three equivalent O(1) and three equivalent O(8) atoms to form FeO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, corners with three equivalent Fe(6)O4 tetrahedra, edges with three equivalent Fe(2)O6 octahedra, and edges with three equivalent Fe(5)O6 octahedra. In the second Fe site, Fe(2) is bonded to one O(2), one O(4), two equivalent O(1), and two equivalent O(3) atoms to form FeO6 octahedra that share  a cornercorner with one Fe(3)O4 tetrahedra,  a cornercorner with one Fe(6)O4 tetrahedra, corners with two equivalent Mg(1)O4 tetrahedra, corners with two equivalent Fe(4)O4 tetrahedra,  an edgeedge with one Fe(1)O6 octahedra, and edges with four equivalent Fe(2)O6 octahedra. In the third Fe site, Fe(3) is bonded to one O(2) and three equivalent O(5) atoms to form corner-sharing FeO4 tetrahedra. The corner-sharing octahedral tilt angles range from 52-59°. In the fourth Fe site, Fe(4) is bonded to one O(7) and three equivalent O(3) atoms to form corner-sharing FeO4 tetrahedra. The corner-sharing octahedral tilt angles range from 56-59°. In the fifth Fe site, Fe(5) is bonded to one O(6), one O(7), two equivalent O(5), and two equivalent O(8) atoms to form FeO6 octahedra that share  a cornercorner with one Mg(1)O4 tetrahedra,  a cornercorner with one Fe(4)O4 tetrahedra, corners with two equivalent Fe(3)O4 tetrahedra, corners with two equivalent Fe(6)O4 tetrahedra,  an edgeedge with one Fe(1)O6 octahedra, and edges with four equivalent Fe(5)O6 octahedra. In the sixth Fe site, Fe(6) is bonded to one O(4) and three equivalent O(8) atoms to form corner-sharing FeO4 tetrahedra. The corner-sharing octahedral tilt angles range from 57-59°. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Fe(1), and two equivalent Fe(2) atoms to form distorted OMgFe3 trigonal pyramids that share corners with two equivalent O(1)MgFe3 trigonal pyramids,  an edgeedge with one O(2)Fe4 trigonal pyramid, and edges with two equivalent O(1)MgFe3 trigonal pyramids. In the second O site, O(2) is bonded to one Fe(3) and three equivalent Fe(2) atoms to form distorted edge-sharing OFe4 trigonal pyramids. In the third O site, O(3) is bonded in a trigonal planar geometry to one Fe(4) and two equivalent Fe(2) atoms. In the fourth O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to one Fe(6) and three equivalent Fe(2) atoms. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Fe(3) and two equivalent Fe(5) atoms. In the sixth O site, O(6) is bonded in a rectangular see-saw-like geometry to one Mg(1) and three equivalent Fe(5) atoms. In the seventh O site, O(7) is bonded in a distorted trigonal pyramidal geometry to one Fe(4) and three equivalent Fe(5) atoms. In the eighth O site, O(8) is bonded in a rectangular see-saw-like geometry to one Fe(1), one Fe(6), and two equivalent Fe(5) atoms.
Mg(Fe5O8)2 is beta indium sulfide-derived structured and crystallizes in the trigonal R3m space group. Mg(1) is bonded to one O(6) and three equivalent O(1) atoms to form MgO4 tetrahedra that share corners with three equivalent Fe(1)O6 octahedra, corners with three equivalent Fe(5)O6 octahedra, and corners with six equivalent Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 55-60°. The Mg(1)-O(6) bond length is 2.03 Å. All Mg(1)-O(1) bond lengths are 2.00 Å. There are six inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to three equivalent O(1) and three equivalent O(8) atoms to form FeO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, corners with three equivalent Fe(6)O4 tetrahedra, edges with three equivalent Fe(2)O6 octahedra, and edges with three equivalent Fe(5)O6 octahedra. All Fe(1)-O(1) bond lengths are 2.00 Å. All Fe(1)-O(8) bond lengths are 2.05 Å. In the second Fe site, Fe(2) is bonded to one O(2), one O(4), two equivalent O(1), and two equivalent O(3) atoms to form FeO6 octahedra that share  a cornercorner with one Fe(3)O4 tetrahedra,  a cornercorner with one Fe(6)O4 tetrahedra, corners with two equivalent Mg(1)O4 tetrahedra, corners with two equivalent Fe(4)O4 tetrahedra,  an edgeedge with one Fe(1)O6 octahedra, and edges with four equivalent Fe(2)O6 octahedra. The Fe(2)-O(2) bond length is 2.01 Å. The Fe(2)-O(4) bond length is 2.05 Å. Both Fe(2)-O(1) bond lengths are 1.99 Å. Both Fe(2)-O(3) bond lengths are 1.93 Å. In the third Fe site, Fe(3) is bonded to one O(2) and three equivalent O(5) atoms to form corner-sharing FeO4 tetrahedra. The corner-sharing octahedral tilt angles range from 52-59°. The Fe(3)-O(2) bond length is 1.94 Å. All Fe(3)-O(5) bond lengths are 1.87 Å. In the fourth Fe site, Fe(4) is bonded to one O(7) and three equivalent O(3) atoms to form corner-sharing FeO4 tetrahedra. The corner-sharing octahedral tilt angles range from 56-59°. The Fe(4)-O(7) bond length is 2.01 Å. All Fe(4)-O(3) bond lengths are 1.90 Å. In the fifth Fe site, Fe(5) is bonded to one O(6), one O(7), two equivalent O(5), and two equivalent O(8) atoms to form FeO6 octahedra that share  a cornercorner with one Mg(1)O4 tetrahedra,  a cornercorner with one Fe(4)O4 tetrahedra, corners with two equivalent Fe(3)O4 tetrahedra, corners with two equivalent Fe(6)O4 tetrahedra,  an edgeedge with one Fe(1)O6 octahedra, and edges with four equivalent Fe(5)O6 octahedra. The Fe(5)-O(6) bond length is 2.04 Å. The Fe(5)-O(7) bond length is 2.06 Å. Both Fe(5)-O(5) bond lengths are 1.96 Å. Both Fe(5)-O(8) bond lengths are 2.13 Å. In the sixth Fe site, Fe(6) is bonded to one O(4) and three equivalent O(8) atoms to form corner-sharing FeO4 tetrahedra. The corner-sharing octahedral tilt angles range from 57-59°. The Fe(6)-O(4) bond length is 1.92 Å. All Fe(6)-O(8) bond lengths are 1.94 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Fe(1), and two equivalent Fe(2) atoms to form distorted OMgFe3 trigonal pyramids that share corners with two equivalent O(1)MgFe3 trigonal pyramids,  an edgeedge with one O(2)Fe4 trigonal pyramid, and edges with two equivalent O(1)MgFe3 trigonal pyramids. In the second O site, O(2) is bonded to one Fe(3) and three equivalent Fe(2) atoms to form distorted edge-sharing OFe4 trigonal pyramids. In the third O site, O(3) is bonded in a trigonal planar geometry to one Fe(4) and two equivalent Fe(2) atoms. In the fourth O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to one Fe(6) and three equivalent Fe(2) atoms. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Fe(3) and two equivalent Fe(5) atoms. In the sixth O site, O(6) is bonded in a rectangular see-saw-like geometry to one Mg(1) and three equivalent Fe(5) atoms. In the seventh O site, O(7) is bonded in a distorted trigonal pyramidal geometry to one Fe(4) and three equivalent Fe(5) atoms. In the eighth O site, O(8) is bonded in a rectangular see-saw-like geometry to one Fe(1), one Fe(6), and two equivalent Fe(5) atoms.