MgFe8(OF)8 crystallizes in the monoclinic Pm space group. Mg(1) is bonded to one O(6), two equivalent O(8), one F(7), and two equivalent F(5) atoms to form MgO3F3 octahedra that share  a cornercorner with one Fe(1)O3F3 octahedra,  a cornercorner with one Fe(5)O3F3 octahedra, corners with two equivalent Fe(6)F6 octahedra, corners with two equivalent Fe(2)O5 square pyramids,  an edgeedge with one Fe(6)F6 octahedra, edges with two equivalent Mg(1)O3F3 octahedra, edges with two equivalent Fe(8)O6 octahedra, and  an edgeedge with one Fe(2)O5 square pyramid. The corner-sharing octahedral tilt angles range from 3-15°. 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  a cornercorner with one Mg(1)O3F3 octahedra, corners with two equivalent Fe(3)O3F3 octahedra, corners with two equivalent Fe(4)O3F3 octahedra, corners with two equivalent Fe(7)O3F3 octahedra, and edges with two equivalent Fe(1)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 9-55°. In the second Fe site, Fe(2) is bonded to one O(4), two equivalent O(1), and two equivalent O(8) atoms to form distorted FeO5 square pyramids that share corners with two equivalent Mg(1)O3F3 octahedra, corners with two equivalent Fe(3)O3F3 octahedra, corners with two equivalent Fe(4)O3F3 octahedra, corners with two equivalent Fe(8)O6 octahedra,  an edgeedge with one Mg(1)O3F3 octahedra, and edges with two equivalent Fe(2)O5 square pyramids. The corner-sharing octahedral tilt angles range from 15-75°. 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)O5 square pyramids, and edges with two equivalent Fe(3)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 48-53°. 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 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)O5 square pyramids, and edges with two equivalent Fe(4)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 46-55°. 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  a cornercorner with one Mg(1)O3F3 octahedra, 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 Fe(5)O3F3 octahedra, and edges with two equivalent Fe(8)O6 octahedra. The corner-sharing octahedral tilt angles range from 15-48°. 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 Mg(1)O3F3 octahedra, corners with two equivalent Fe(3)O3F3 octahedra, corners with two equivalent Fe(4)O3F3 octahedra, corners with two equivalent Fe(7)O3F3 octahedra,  an edgeedge with one Mg(1)O3F3 octahedra, and edges with two equivalent Fe(6)F6 octahedra. The corner-sharing octahedral tilt angles range from 3-48°. 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(8)O6 octahedra, edges with two equivalent Fe(7)O3F3 octahedra, and  a faceface with one Fe(8)O6 octahedra. The corner-sharing octahedral tilt angles range from 40-48°. In the eighth Fe site, Fe(8) is bonded to one O(5), one O(8), two equivalent O(6), and two equivalent O(7) atoms to form FeO6 octahedra that share corners with two equivalent Fe(7)O3F3 octahedra, corners with two equivalent Fe(2)O5 square pyramids, edges with two equivalent Mg(1)O3F3 octahedra, edges with two equivalent Fe(5)O3F3 octahedra, edges with two equivalent Fe(8)O6 octahedra, and  a faceface with one Fe(7)O3F3 octahedra. The corner-sharing octahedral tilt angles are 40°. 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 in a trigonal planar geometry to one Fe(4) and two equivalent Fe(1) atoms. 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 in a trigonal planar geometry to one Fe(2) and two equivalent Fe(4) atoms. In the fifth O site, O(5) is bonded to one Fe(7), one Fe(8), and two equivalent Fe(5) atoms to form OFe4 trigonal pyramids that share  a cornercorner with one O(8)Mg2Fe3 square pyramid and corners with two equivalent O(5)Fe4 trigonal pyramids. In the sixth O site, O(6) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Fe(5), and two equivalent Fe(8) atoms. In the seventh O site, O(7) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Fe(7) and two equivalent Fe(8) atoms. In the eighth O site, O(8) is bonded to two equivalent Mg(1), one Fe(8), and two equivalent Fe(2) atoms to form OMg2Fe3 square pyramids that share  a cornercorner with one O(5)Fe4 trigonal pyramid and edges with two equivalent O(8)Mg2Fe3 square pyramids. 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 T-shaped geometry to one Fe(4) and two equivalent Fe(5) atoms. In the fifth F site, F(5) is bonded in a rectangular see-saw-like geometry to two equivalent Mg(1) 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 linear geometry to one Mg(1) and one Fe(1) atom. In the eighth F site, F(8) is bonded in a distorted T-shaped 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(6), two equivalent O(8), one F(7), and two equivalent F(5) atoms to form MgO3F3 octahedra that share  a cornercorner with one Fe(1)O3F3 octahedra,  a cornercorner with one Fe(5)O3F3 octahedra, corners with two equivalent Fe(6)F6 octahedra, corners with two equivalent Fe(2)O5 square pyramids,  an edgeedge with one Fe(6)F6 octahedra, edges with two equivalent Mg(1)O3F3 octahedra, edges with two equivalent Fe(8)O6 octahedra, and  an edgeedge with one Fe(2)O5 square pyramid. The corner-sharing octahedral tilt angles range from 3-15°. The Mg(1)-O(6) bond length is 2.01 Å. Both Mg(1)-O(8) bond lengths are 2.27 Å. The Mg(1)-F(7) bond length is 1.88 Å. Both Mg(1)-F(5) bond lengths are 2.19 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  a cornercorner with one Mg(1)O3F3 octahedra, corners with two equivalent Fe(3)O3F3 octahedra, corners with two equivalent Fe(4)O3F3 octahedra, corners with two equivalent Fe(7)O3F3 octahedra, and edges with two equivalent Fe(1)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 9-55°. The Fe(1)-O(3) bond length is 1.93 Å. Both Fe(1)-O(2) bond lengths are 1.93 Å. The Fe(1)-F(7) bond length is 1.97 Å. Both Fe(1)-F(8) bond lengths are 2.16 Å. In the second Fe site, Fe(2) is bonded to one O(4), two equivalent O(1), and two equivalent O(8) atoms to form distorted FeO5 square pyramids that share corners with two equivalent Mg(1)O3F3 octahedra, corners with two equivalent Fe(3)O3F3 octahedra, corners with two equivalent Fe(4)O3F3 octahedra, corners with two equivalent Fe(8)O6 octahedra,  an edgeedge with one Mg(1)O3F3 octahedra, and edges with two equivalent Fe(2)O5 square pyramids. The corner-sharing octahedral tilt angles range from 15-75°. The Fe(2)-O(4) bond length is 1.90 Å. Both Fe(2)-O(1) bond lengths are 1.96 Å. Both Fe(2)-O(8) bond lengths are 2.18 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)O5 square pyramids, and edges with two equivalent Fe(3)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 48-53°. The Fe(3)-O(1) bond length is 1.95 Å. Both Fe(3)-O(3) bond lengths are 1.93 Å. The Fe(3)-F(3) bond length is 2.35 Å. Both Fe(3)-F(1) bond lengths are 2.11 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 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)O5 square pyramids, and edges with two equivalent Fe(4)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 46-55°. The Fe(4)-O(2) bond length is 1.91 Å. Both Fe(4)-O(4) bond lengths are 1.94 Å. The Fe(4)-F(4) bond length is 2.00 Å. Both Fe(4)-F(2) bond lengths are 2.19 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  a cornercorner with one Mg(1)O3F3 octahedra, 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 Fe(5)O3F3 octahedra, and edges with two equivalent Fe(8)O6 octahedra. The corner-sharing octahedral tilt angles range from 15-48°. The Fe(5)-O(6) bond length is 2.16 Å. Both Fe(5)-O(5) bond lengths are 2.08 Å. The Fe(5)-F(1) bond length is 2.11 Å. Both Fe(5)-F(4) bond lengths are 2.12 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 Mg(1)O3F3 octahedra, corners with two equivalent Fe(3)O3F3 octahedra, corners with two equivalent Fe(4)O3F3 octahedra, corners with two equivalent Fe(7)O3F3 octahedra,  an edgeedge with one Mg(1)O3F3 octahedra, and edges with two equivalent Fe(6)F6 octahedra. The corner-sharing octahedral tilt angles range from 3-48°. The Fe(6)-F(2) bond length is 2.05 Å. The Fe(6)-F(6) bond length is 2.12 Å. Both Fe(6)-F(3) bond lengths are 2.07 Å. Both Fe(6)-F(5) bond lengths are 2.29 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(8)O6 octahedra, edges with two equivalent Fe(7)O3F3 octahedra, and  a faceface with one Fe(8)O6 octahedra. The corner-sharing octahedral tilt angles range from 40-48°. The Fe(7)-O(5) bond length is 1.90 Å. Both Fe(7)-O(7) bond lengths are 2.06 Å. The Fe(7)-F(8) bond length is 1.99 Å. Both Fe(7)-F(6) bond lengths are 2.12 Å. In the eighth Fe site, Fe(8) is bonded to one O(5), one O(8), two equivalent O(6), and two equivalent O(7) atoms to form FeO6 octahedra that share corners with two equivalent Fe(7)O3F3 octahedra, corners with two equivalent Fe(2)O5 square pyramids, edges with two equivalent Mg(1)O3F3 octahedra, edges with two equivalent Fe(5)O3F3 octahedra, edges with two equivalent Fe(8)O6 octahedra, and  a faceface with one Fe(7)O3F3 octahedra. The corner-sharing octahedral tilt angles are 40°. The Fe(8)-O(5) bond length is 2.03 Å. The Fe(8)-O(8) bond length is 2.01 Å. Both Fe(8)-O(6) bond lengths are 1.98 Å. Both Fe(8)-O(7) bond lengths are 2.22 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 in a trigonal planar geometry to one Fe(4) and two equivalent Fe(1) atoms. 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 in a trigonal planar geometry to one Fe(2) and two equivalent Fe(4) atoms. In the fifth O site, O(5) is bonded to one Fe(7), one Fe(8), and two equivalent Fe(5) atoms to form OFe4 trigonal pyramids that share  a cornercorner with one O(8)Mg2Fe3 square pyramid and corners with two equivalent O(5)Fe4 trigonal pyramids. In the sixth O site, O(6) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Fe(5), and two equivalent Fe(8) atoms. In the seventh O site, O(7) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Fe(7) and two equivalent Fe(8) atoms. In the eighth O site, O(8) is bonded to two equivalent Mg(1), one Fe(8), and two equivalent Fe(2) atoms to form OMg2Fe3 square pyramids that share  a cornercorner with one O(5)Fe4 trigonal pyramid and edges with two equivalent O(8)Mg2Fe3 square pyramids. 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 T-shaped geometry to one Fe(4) and two equivalent Fe(5) atoms. In the fifth F site, F(5) is bonded in a rectangular see-saw-like geometry to two equivalent Mg(1) 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 linear geometry to one Mg(1) and one Fe(1) atom. In the eighth F site, F(8) is bonded in a distorted T-shaped geometry to one Fe(7) and two equivalent Fe(1) atoms.