MgFe8(OF)8 crystallizes in the monoclinic Pm space group. Mg(1) is bonded to one O(3), one O(7), two equivalent O(1), and two equivalent F(8) atoms to form MgO4F2 octahedra that share corners with two equivalent Fe(2)O6 octahedra,  a cornercorner with one Fe(1)O3F tetrahedra, edges with two equivalent Mg(1)O4F2 octahedra, edges with two equivalent Fe(3)O3F3 octahedra, edges with two equivalent Fe(7)O3F3 octahedra, and  a faceface with one Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles are 44°. There are eight inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(3), two equivalent O(2), and one F(7) atom to form distorted FeO3F tetrahedra that share  a cornercorner with one Mg(1)O4F2 octahedra, corners with two equivalent Fe(3)O3F3 octahedra, corners with two equivalent Fe(4)O3F3 octahedra, corners with two equivalent Fe(8)O3F3 octahedra, and corners with two equivalent Fe(1)O3F tetrahedra. The corner-sharing octahedral tilt angles range from 52-91°. 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 distorted FeO6 octahedra that share corners with two equivalent Mg(1)O4F2 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, corners with two equivalent Fe(8)O3F3 octahedra, edges with two equivalent Fe(2)O6 octahedra, and  a faceface with one Mg(1)O4F2 octahedra. The corner-sharing octahedral tilt angles range from 44-57°. 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 FeO3F3 octahedra that share corners with two equivalent Fe(6)F6 octahedra, corners with two equivalent Fe(5)O3F3 octahedra, corners with two equivalent Fe(2)O6 octahedra, corners with two equivalent Fe(1)O3F tetrahedra, edges with two equivalent Mg(1)O4F2 octahedra, and edges with two equivalent Fe(3)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 47-48°. 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(5)O3F3 octahedra, corners with two equivalent Fe(2)O6 octahedra, corners with two equivalent Fe(1)O3F tetrahedra, and edges with two equivalent Fe(4)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 47-57°. 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 a mixture of edge and corner-sharing FeO3F3 octahedra. The corner-sharing octahedral tilt angles range from 48-55°. 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)O3F3 octahedra, and edges with two equivalent Fe(6)F6 octahedra. The corner-sharing octahedral tilt angles range from 47-48°. 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 distorted FeO3F3 octahedra that share corners with two equivalent Fe(6)F6 octahedra, corners with two equivalent Fe(5)O3F3 octahedra, corners with two equivalent Fe(2)O6 octahedra, edges with two equivalent Mg(1)O4F2 octahedra, and edges with two equivalent Fe(7)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 48-55°. In the eighth Fe site, Fe(8) is bonded to one O(8), two equivalent O(6), one F(5), and two equivalent F(7) atoms to form FeO3F3 octahedra that share corners with two equivalent Fe(6)F6 octahedra, corners with two equivalent Fe(5)O3F3 octahedra, corners with two equivalent Fe(2)O6 octahedra, corners with two equivalent Fe(1)O3F tetrahedra, and edges with two equivalent Fe(8)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 48-53°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to two equivalent Mg(1), 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 to one Mg(1), one Fe(1), and two equivalent Fe(3) atoms to form corner-sharing OMgFe3 trigonal pyramids. 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 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 to one Mg(1), one Fe(2), and two equivalent Fe(7) atoms to form distorted corner-sharing OMgFe3 trigonal pyramids. In the eighth O site, O(8) is bonded in a trigonal planar geometry to 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 trigonal planar 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 T-shaped 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 trigonal planar geometry to one Fe(8) and two equivalent Fe(6) atoms. In the sixth F site, F(6) is bonded in a distorted trigonal planar geometry to one Fe(6) and two equivalent Fe(7) atoms. In the seventh F site, F(7) is bonded in a distorted trigonal planar geometry to one Fe(1) and two equivalent Fe(8) atoms. In the eighth F site, F(8) is bonded in a 3-coordinate geometry to two equivalent Mg(1) and one Fe(7) atom.
MgFe8(OF)8 crystallizes in the monoclinic Pm space group. Mg(1) is bonded to one O(3), one O(7), two equivalent O(1), and two equivalent F(8) atoms to form MgO4F2 octahedra that share corners with two equivalent Fe(2)O6 octahedra,  a cornercorner with one Fe(1)O3F tetrahedra, edges with two equivalent Mg(1)O4F2 octahedra, edges with two equivalent Fe(3)O3F3 octahedra, edges with two equivalent Fe(7)O3F3 octahedra, and  a faceface with one Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles are 44°. The Mg(1)-O(3) bond length is 1.98 Å. The Mg(1)-O(7) bond length is 1.98 Å. Both Mg(1)-O(1) bond lengths are 2.12 Å. Both Mg(1)-F(8) bond lengths are 2.05 Å. There are eight inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(3), two equivalent O(2), and one F(7) atom to form distorted FeO3F tetrahedra that share  a cornercorner with one Mg(1)O4F2 octahedra, corners with two equivalent Fe(3)O3F3 octahedra, corners with two equivalent Fe(4)O3F3 octahedra, corners with two equivalent Fe(8)O3F3 octahedra, and corners with two equivalent Fe(1)O3F tetrahedra. The corner-sharing octahedral tilt angles range from 52-91°. The Fe(1)-O(3) bond length is 2.09 Å. Both Fe(1)-O(2) bond lengths are 1.91 Å. The Fe(1)-F(7) bond length is 2.15 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 distorted FeO6 octahedra that share corners with two equivalent Mg(1)O4F2 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, corners with two equivalent Fe(8)O3F3 octahedra, edges with two equivalent Fe(2)O6 octahedra, and  a faceface with one Mg(1)O4F2 octahedra. The corner-sharing octahedral tilt angles range from 44-57°. The Fe(2)-O(4) bond length is 1.90 Å. The Fe(2)-O(7) bond length is 2.17 Å. Both Fe(2)-O(1) bond lengths are 2.34 Å. Both Fe(2)-O(8) bond lengths are 1.97 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 FeO3F3 octahedra that share corners with two equivalent Fe(6)F6 octahedra, corners with two equivalent Fe(5)O3F3 octahedra, corners with two equivalent Fe(2)O6 octahedra, corners with two equivalent Fe(1)O3F tetrahedra, edges with two equivalent Mg(1)O4F2 octahedra, and edges with two equivalent Fe(3)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 47-48°. The Fe(3)-O(1) bond length is 2.03 Å. Both Fe(3)-O(3) bond lengths are 1.99 Å. The Fe(3)-F(3) bond length is 2.18 Å. Both Fe(3)-F(1) bond lengths are 2.09 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(5)O3F3 octahedra, corners with two equivalent Fe(2)O6 octahedra, corners with two equivalent Fe(1)O3F tetrahedra, and edges with two equivalent Fe(4)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 47-57°. The Fe(4)-O(2) bond length is 1.86 Å. Both Fe(4)-O(4) bond lengths are 1.95 Å. The Fe(4)-F(4) bond length is 2.14 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 a mixture of edge and corner-sharing FeO3F3 octahedra. The corner-sharing octahedral tilt angles range from 48-55°. The Fe(5)-O(6) bond length is 1.90 Å. Both Fe(5)-O(5) bond lengths are 1.96 Å. The Fe(5)-F(1) bond length is 2.22 Å. Both Fe(5)-F(4) bond lengths are 2.09 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)O3F3 octahedra, and edges with two equivalent Fe(6)F6 octahedra. The corner-sharing octahedral tilt angles range from 47-48°. The Fe(6)-F(2) bond length is 2.09 Å. The Fe(6)-F(6) bond length is 2.14 Å. Both Fe(6)-F(3) bond lengths are 2.14 Å. Both Fe(6)-F(5) bond lengths are 2.11 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 distorted FeO3F3 octahedra that share corners with two equivalent Fe(6)F6 octahedra, corners with two equivalent Fe(5)O3F3 octahedra, corners with two equivalent Fe(2)O6 octahedra, edges with two equivalent Mg(1)O4F2 octahedra, and edges with two equivalent Fe(7)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 48-55°. The Fe(7)-O(5) bond length is 1.89 Å. Both Fe(7)-O(7) bond lengths are 1.97 Å. The Fe(7)-F(8) bond length is 2.30 Å. Both Fe(7)-F(6) bond lengths are 2.11 Å. In the eighth Fe site, Fe(8) is bonded to one O(8), two equivalent O(6), one F(5), and two equivalent F(7) atoms to form FeO3F3 octahedra that share corners with two equivalent Fe(6)F6 octahedra, corners with two equivalent Fe(5)O3F3 octahedra, corners with two equivalent Fe(2)O6 octahedra, corners with two equivalent Fe(1)O3F tetrahedra, and edges with two equivalent Fe(8)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 48-53°. The Fe(8)-O(8) bond length is 1.94 Å. Both Fe(8)-O(6) bond lengths are 1.96 Å. The Fe(8)-F(5) bond length is 2.21 Å. Both Fe(8)-F(7) bond lengths are 2.14 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to two equivalent Mg(1), 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 to one Mg(1), one Fe(1), and two equivalent Fe(3) atoms to form corner-sharing OMgFe3 trigonal pyramids. 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 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 to one Mg(1), one Fe(2), and two equivalent Fe(7) atoms to form distorted corner-sharing OMgFe3 trigonal pyramids. In the eighth O site, O(8) is bonded in a trigonal planar geometry to 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 trigonal planar 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 T-shaped 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 trigonal planar geometry to one Fe(8) and two equivalent Fe(6) atoms. In the sixth F site, F(6) is bonded in a distorted trigonal planar geometry to one Fe(6) and two equivalent Fe(7) atoms. In the seventh F site, F(7) is bonded in a distorted trigonal planar geometry to one Fe(1) and two equivalent Fe(8) atoms. In the eighth F site, F(8) is bonded in a 3-coordinate geometry to two equivalent Mg(1) and one Fe(7) atom.