MgFe8(OF)8 crystallizes in the monoclinic Pm space group. Mg(1) is bonded to one O(2), one O(8), two equivalent O(4), and two equivalent F(7) atoms to form MgO4F2 octahedra that share corners with two equivalent Fe(4)O3F3 octahedra,  a cornercorner with one Fe(8)O3F tetrahedra, edges with two equivalent Mg(1)O4F2 octahedra, edges with two equivalent Fe(1)O3F3 octahedra, edges with two equivalent Fe(2)O6 octahedra, and  a faceface with one Fe(4)O3F3 octahedra. The corner-sharing octahedral tilt angles are 45°. There are eight inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(3), two equivalent O(2), one F(7), and two equivalent F(8) atoms to form FeO3F3 octahedra that share corners with two equivalent Fe(3)O3F3 octahedra, corners with two equivalent Fe(4)O3F3 octahedra, corners with two equivalent Fe(7)O3F3 octahedra, edges with two equivalent Mg(1)O4F2 octahedra, and edges with two equivalent Fe(1)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 48-54°. In the second Fe site, Fe(2) is bonded to one O(4), one O(7), two equivalent O(1), and two equivalent O(8) atoms to form FeO6 octahedra that share corners with two equivalent Fe(3)O3F3 octahedra, corners with two equivalent Fe(4)O3F3 octahedra, corners with two equivalent Fe(7)O3F3 octahedra, corners with two equivalent Fe(8)O3F tetrahedra, edges with two equivalent Mg(1)O4F2 octahedra, and edges with two equivalent Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 50-53°. In the third Fe site, Fe(3) is bonded to one O(1), two equivalent O(3), one F(3), and two equivalent F(1) atoms to form distorted FeO3F3 octahedra that share corners with two equivalent Fe(6)F6 octahedra, corners with two equivalent Fe(1)O3F3 octahedra, corners with two equivalent Fe(5)O3F3 octahedra, corners with two equivalent Fe(2)O6 octahedra, and edges with two equivalent Fe(3)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 47-54°. In the fourth Fe site, Fe(4) is bonded to one O(2), two equivalent O(4), one F(4), and two equivalent F(2) atoms to form distorted FeO3F3 octahedra that share corners with two equivalent Mg(1)O4F2 octahedra, corners with two equivalent Fe(6)F6 octahedra, corners with two equivalent Fe(1)O3F3 octahedra, corners with two equivalent Fe(5)O3F3 octahedra, corners with two equivalent Fe(2)O6 octahedra, edges with two equivalent Fe(4)O3F3 octahedra, and  a faceface with one Mg(1)O4F2 octahedra. The corner-sharing octahedral tilt angles range from 45-53°. In the fifth Fe site, Fe(5) is bonded to one O(6), two equivalent O(5), one F(1), and two equivalent F(4) atoms to form FeO3F3 octahedra that share corners with two equivalent Fe(3)O3F3 octahedra, corners with two equivalent Fe(4)O3F3 octahedra, corners with two equivalent Fe(7)O3F3 octahedra, corners with two equivalent Fe(8)O3F tetrahedra, and edges with two equivalent Fe(5)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 47-55°. In the sixth Fe site, Fe(6) is bonded to one F(2), one F(6), two equivalent F(3), and two equivalent F(5) atoms to form FeF6 octahedra that share corners with two equivalent Fe(3)O3F3 octahedra, corners with two equivalent Fe(4)O3F3 octahedra, corners with two equivalent Fe(7)O3F3 octahedra, corners with two equivalent Fe(8)O3F tetrahedra, and edges with two equivalent Fe(6)F6 octahedra. The corner-sharing octahedral tilt angles range from 46-49°. In the seventh Fe site, Fe(7) is bonded to one O(5), two equivalent O(7), one F(8), and two equivalent F(6) atoms to form FeO3F3 octahedra that share corners with two equivalent Fe(6)F6 octahedra, corners with two equivalent Fe(1)O3F3 octahedra, corners with two equivalent Fe(5)O3F3 octahedra, corners with two equivalent Fe(2)O6 octahedra, and edges with two equivalent Fe(7)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 46-55°. In the eighth Fe site, Fe(8) is bonded to one O(8), two equivalent O(6), and one F(5) atom to form FeO3F tetrahedra that share  a cornercorner with one Mg(1)O4F2 octahedra, corners with two equivalent Fe(6)F6 octahedra, corners with two equivalent Fe(5)O3F3 octahedra, corners with two equivalent Fe(2)O6 octahedra, and corners with two equivalent Fe(8)O3F tetrahedra. The corner-sharing octahedral tilt angles range from 48-75°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Fe(3) and two equivalent Fe(2) atoms. In the second O site, O(2) is bonded to one Mg(1), one Fe(4), and two equivalent Fe(1) atoms to form distorted OMgFe3 trigonal pyramids that share corners with two equivalent O(2)MgFe3 trigonal pyramids and edges with two equivalent O(4)Mg2Fe3 square pyramids. In the third O site, O(3) is bonded in a trigonal planar geometry to one Fe(1) and two equivalent Fe(3) atoms. In the fourth O site, O(4) is bonded to two equivalent Mg(1), one Fe(2), and two equivalent Fe(4) atoms to form distorted OMg2Fe3 square pyramids that share edges with two equivalent O(4)Mg2Fe3 square pyramids and edges with two equivalent O(2)MgFe3 trigonal pyramids. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Fe(7) and two equivalent Fe(5) atoms. In the sixth O site, O(6) is bonded in a trigonal planar geometry to one Fe(5) and two equivalent Fe(8) atoms. In the seventh O site, O(7) is bonded in a trigonal planar geometry to one Fe(2) and two equivalent Fe(7) atoms. In the eighth O site, O(8) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Fe(8), and two equivalent Fe(2) atoms. There are eight inequivalent F sites. In the first F site, F(1) is bonded in a distorted T-shaped geometry to one Fe(5) and two equivalent Fe(3) atoms. In the second F site, F(2) is bonded in a distorted T-shaped geometry to one Fe(6) and two equivalent Fe(4) atoms. In the third F site, F(3) is bonded in a distorted trigonal planar geometry to one Fe(3) and two equivalent Fe(6) atoms. In the fourth F site, F(4) is bonded in a distorted trigonal planar geometry to one Fe(4) and two equivalent Fe(5) atoms. In the fifth F site, F(5) is bonded in a distorted T-shaped geometry to one Fe(8) and two equivalent Fe(6) atoms. In the sixth F site, F(6) is bonded in a distorted T-shaped geometry to one Fe(6) and two equivalent Fe(7) atoms. In the seventh F site, F(7) is bonded in a distorted T-shaped geometry to two equivalent Mg(1) and one Fe(1) atom. In the eighth F site, F(8) is bonded in a distorted trigonal planar geometry to one Fe(7) and two equivalent Fe(1) atoms.
MgFe8(OF)8 crystallizes in the monoclinic Pm space group. Mg(1) is bonded to one O(2), one O(8), two equivalent O(4), and two equivalent F(7) atoms to form MgO4F2 octahedra that share corners with two equivalent Fe(4)O3F3 octahedra,  a cornercorner with one Fe(8)O3F tetrahedra, edges with two equivalent Mg(1)O4F2 octahedra, edges with two equivalent Fe(1)O3F3 octahedra, edges with two equivalent Fe(2)O6 octahedra, and  a faceface with one Fe(4)O3F3 octahedra. The corner-sharing octahedral tilt angles are 45°. The Mg(1)-O(2) bond length is 2.01 Å. The Mg(1)-O(8) bond length is 1.97 Å. Both Mg(1)-O(4) bond lengths are 2.11 Å. Both Mg(1)-F(7) bond lengths are 2.07 Å. There are eight inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(3), two equivalent O(2), one F(7), and two equivalent F(8) atoms to form FeO3F3 octahedra that share corners with two equivalent Fe(3)O3F3 octahedra, corners with two equivalent Fe(4)O3F3 octahedra, corners with two equivalent Fe(7)O3F3 octahedra, edges with two equivalent Mg(1)O4F2 octahedra, and edges with two equivalent Fe(1)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 48-54°. The Fe(1)-O(3) bond length is 1.87 Å. Both Fe(1)-O(2) bond lengths are 1.95 Å. The Fe(1)-F(7) bond length is 2.20 Å. Both Fe(1)-F(8) bond lengths are 2.13 Å. In the second Fe site, Fe(2) is bonded to one O(4), one O(7), two equivalent O(1), and two equivalent O(8) atoms to form FeO6 octahedra that share corners with two equivalent Fe(3)O3F3 octahedra, corners with two equivalent Fe(4)O3F3 octahedra, corners with two equivalent Fe(7)O3F3 octahedra, corners with two equivalent Fe(8)O3F tetrahedra, edges with two equivalent Mg(1)O4F2 octahedra, and edges with two equivalent Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 50-53°. The Fe(2)-O(4) bond length is 2.09 Å. The Fe(2)-O(7) bond length is 2.05 Å. Both Fe(2)-O(1) bond lengths are 1.98 Å. Both Fe(2)-O(8) bond lengths are 2.20 Å. In the third Fe site, Fe(3) is bonded to one O(1), two equivalent O(3), one F(3), and two equivalent F(1) atoms to form distorted FeO3F3 octahedra that share corners with two equivalent Fe(6)F6 octahedra, corners with two equivalent Fe(1)O3F3 octahedra, corners with two equivalent Fe(5)O3F3 octahedra, corners with two equivalent Fe(2)O6 octahedra, and edges with two equivalent Fe(3)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 47-54°. The Fe(3)-O(1) bond length is 1.89 Å. Both Fe(3)-O(3) bond lengths are 1.93 Å. The Fe(3)-F(3) bond length is 2.31 Å. Both Fe(3)-F(1) bond lengths are 2.12 Å. In the fourth Fe site, Fe(4) is bonded to one O(2), two equivalent O(4), one F(4), and two equivalent F(2) atoms to form distorted FeO3F3 octahedra that share corners with two equivalent Mg(1)O4F2 octahedra, corners with two equivalent Fe(6)F6 octahedra, corners with two equivalent Fe(1)O3F3 octahedra, corners with two equivalent Fe(5)O3F3 octahedra, corners with two equivalent Fe(2)O6 octahedra, edges with two equivalent Fe(4)O3F3 octahedra, and  a faceface with one Mg(1)O4F2 octahedra. The corner-sharing octahedral tilt angles range from 45-53°. The Fe(4)-O(2) bond length is 2.13 Å. Both Fe(4)-O(4) bond lengths are 2.26 Å. The Fe(4)-F(4) bond length is 2.09 Å. Both Fe(4)-F(2) bond lengths are 2.17 Å. In the fifth Fe site, Fe(5) is bonded to one O(6), two equivalent O(5), one F(1), and two equivalent F(4) atoms to form FeO3F3 octahedra that share corners with two equivalent Fe(3)O3F3 octahedra, corners with two equivalent Fe(4)O3F3 octahedra, corners with two equivalent Fe(7)O3F3 octahedra, corners with two equivalent Fe(8)O3F tetrahedra, and edges with two equivalent Fe(5)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 47-55°. The Fe(5)-O(6) bond length is 1.95 Å. Both Fe(5)-O(5) bond lengths are 1.93 Å. The Fe(5)-F(1) bond length is 2.02 Å. Both Fe(5)-F(4) bond lengths are 2.14 Å. In the sixth Fe site, Fe(6) is bonded to one F(2), one F(6), two equivalent F(3), and two equivalent F(5) atoms to form FeF6 octahedra that share corners with two equivalent Fe(3)O3F3 octahedra, corners with two equivalent Fe(4)O3F3 octahedra, corners with two equivalent Fe(7)O3F3 octahedra, corners with two equivalent Fe(8)O3F tetrahedra, and edges with two equivalent Fe(6)F6 octahedra. The corner-sharing octahedral tilt angles range from 46-49°. The Fe(6)-F(2) bond length is 2.16 Å. The Fe(6)-F(6) bond length is 2.20 Å. Both Fe(6)-F(3) bond lengths are 2.07 Å. Both Fe(6)-F(5) bond lengths are 2.18 Å. In the seventh Fe site, Fe(7) is bonded to one O(5), two equivalent O(7), one F(8), and two equivalent F(6) atoms to form FeO3F3 octahedra that share corners with two equivalent Fe(6)F6 octahedra, corners with two equivalent Fe(1)O3F3 octahedra, corners with two equivalent Fe(5)O3F3 octahedra, corners with two equivalent Fe(2)O6 octahedra, and edges with two equivalent Fe(7)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 46-55°. The Fe(7)-O(5) bond length is 1.97 Å. Both Fe(7)-O(7) bond lengths are 1.94 Å. The Fe(7)-F(8) bond length is 2.08 Å. Both Fe(7)-F(6) bond lengths are 2.20 Å. In the eighth Fe site, Fe(8) is bonded to one O(8), two equivalent O(6), and one F(5) atom to form FeO3F tetrahedra that share  a cornercorner with one Mg(1)O4F2 octahedra, corners with two equivalent Fe(6)F6 octahedra, corners with two equivalent Fe(5)O3F3 octahedra, corners with two equivalent Fe(2)O6 octahedra, and corners with two equivalent Fe(8)O3F tetrahedra. The corner-sharing octahedral tilt angles range from 48-75°. The Fe(8)-O(8) bond length is 1.85 Å. Both Fe(8)-O(6) bond lengths are 1.87 Å. The Fe(8)-F(5) bond length is 2.01 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Fe(3) and two equivalent Fe(2) atoms. In the second O site, O(2) is bonded to one Mg(1), one Fe(4), and two equivalent Fe(1) atoms to form distorted OMgFe3 trigonal pyramids that share corners with two equivalent O(2)MgFe3 trigonal pyramids and edges with two equivalent O(4)Mg2Fe3 square pyramids. In the third O site, O(3) is bonded in a trigonal planar geometry to one Fe(1) and two equivalent Fe(3) atoms. In the fourth O site, O(4) is bonded to two equivalent Mg(1), one Fe(2), and two equivalent Fe(4) atoms to form distorted OMg2Fe3 square pyramids that share edges with two equivalent O(4)Mg2Fe3 square pyramids and edges with two equivalent O(2)MgFe3 trigonal pyramids. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Fe(7) and two equivalent Fe(5) atoms. In the sixth O site, O(6) is bonded in a trigonal planar geometry to one Fe(5) and two equivalent Fe(8) atoms. In the seventh O site, O(7) is bonded in a trigonal planar geometry to one Fe(2) and two equivalent Fe(7) atoms. In the eighth O site, O(8) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Fe(8), and two equivalent Fe(2) atoms. There are eight inequivalent F sites. In the first F site, F(1) is bonded in a distorted T-shaped geometry to one Fe(5) and two equivalent Fe(3) atoms. In the second F site, F(2) is bonded in a distorted T-shaped geometry to one Fe(6) and two equivalent Fe(4) atoms. In the third F site, F(3) is bonded in a distorted trigonal planar geometry to one Fe(3) and two equivalent Fe(6) atoms. In the fourth F site, F(4) is bonded in a distorted trigonal planar geometry to one Fe(4) and two equivalent Fe(5) atoms. In the fifth F site, F(5) is bonded in a distorted T-shaped geometry to one Fe(8) and two equivalent Fe(6) atoms. In the sixth F site, F(6) is bonded in a distorted T-shaped geometry to one Fe(6) and two equivalent Fe(7) atoms. In the seventh F site, F(7) is bonded in a distorted T-shaped geometry to two equivalent Mg(1) and one Fe(1) atom. In the eighth F site, F(8) is bonded in a distorted trigonal planar geometry to one Fe(7) and two equivalent Fe(1) atoms.