MgFe8(OF)8 crystallizes in the monoclinic Pm space group. Mg(1) is bonded to one F(6), one F(7), two equivalent F(5), and two equivalent F(8) atoms to form distorted MgF6 octahedra that share corners with two equivalent Fe(6)F6 octahedra, edges with two equivalent Mg(1)F6 octahedra, and  a faceface with one Fe(6)F6 octahedra. The corner-sharing octahedral tilt angles are 34°. There are eight inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a trigonal planar geometry to one O(3) and two equivalent O(2) atoms. 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, and edges with two equivalent Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 51-56°. 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(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 46-51°. 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 Fe(6)F6 octahedra, corners with two equivalent Fe(5)O3F3 octahedra, corners with two equivalent Fe(2)O6 octahedra, and edges with two equivalent Fe(4)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 47-56°. 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 46-47°. 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 distorted FeF6 octahedra that share corners with two equivalent Mg(1)F6 octahedra, corners with two equivalent Fe(3)O3F3 octahedra, corners with two equivalent Fe(4)O3F3 octahedra, edges with two equivalent Fe(6)F6 octahedra, and  a faceface with one Mg(1)F6 octahedra. The corner-sharing octahedral tilt angles range from 34-51°. In the seventh Fe site, Fe(7) is bonded in a 6-coordinate geometry to one O(5), two equivalent O(7), one F(8), and two equivalent F(6) atoms. In the eighth Fe site, Fe(8) is bonded in a 5-coordinate geometry to one O(8), two equivalent O(6), and two equivalent F(7) atoms. 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 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 distorted 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 T-shaped geometry to one Fe(5) and two equivalent Fe(3) atoms. In the second F site, F(2) is bonded in a 3-coordinate 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 distorted 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 rectangular see-saw-like geometry to one Mg(1), 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 Mg(1) and two equivalent Fe(8) atoms. In the eighth F site, F(8) is bonded in a distorted trigonal non-coplanar 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 F(6), one F(7), two equivalent F(5), and two equivalent F(8) atoms to form distorted MgF6 octahedra that share corners with two equivalent Fe(6)F6 octahedra, edges with two equivalent Mg(1)F6 octahedra, and  a faceface with one Fe(6)F6 octahedra. The corner-sharing octahedral tilt angles are 34°. The Mg(1)-F(6) bond length is 2.02 Å. The Mg(1)-F(7) bond length is 1.93 Å. Both Mg(1)-F(5) bond lengths are 2.18 Å. Both Mg(1)-F(8) bond lengths are 1.95 Å. There are eight inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a trigonal planar geometry to one O(3) and two equivalent O(2) atoms. The Fe(1)-O(3) bond length is 1.89 Å. Both Fe(1)-O(2) bond lengths are 1.91 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, and edges with two equivalent Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 51-56°. The Fe(2)-O(4) bond length is 2.00 Å. The Fe(2)-O(7) bond length is 2.08 Å. Both Fe(2)-O(1) bond lengths are 2.01 Å. Both Fe(2)-O(8) bond lengths are 2.08 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(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 46-51°. The Fe(3)-O(1) bond length is 1.86 Å. Both Fe(3)-O(3) bond lengths are 1.94 Å. The Fe(3)-F(3) bond length is 2.43 Å. Both Fe(3)-F(1) bond lengths are 2.18 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 Fe(6)F6 octahedra, corners with two equivalent Fe(5)O3F3 octahedra, corners with two equivalent Fe(2)O6 octahedra, and edges with two equivalent Fe(4)O3F3 octahedra. The corner-sharing octahedral tilt angles range from 47-56°. The Fe(4)-O(2) bond length is 1.92 Å. Both Fe(4)-O(4) bond lengths are 1.90 Å. The Fe(4)-F(4) bond length is 2.18 Å. Both Fe(4)-F(2) bond lengths are 2.29 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 46-47°. The Fe(5)-O(6) bond length is 1.93 Å. Both Fe(5)-O(5) bond lengths are 1.97 Å. The Fe(5)-F(1) bond length is 2.07 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 distorted FeF6 octahedra that share corners with two equivalent Mg(1)F6 octahedra, corners with two equivalent Fe(3)O3F3 octahedra, corners with two equivalent Fe(4)O3F3 octahedra, edges with two equivalent Fe(6)F6 octahedra, and  a faceface with one Mg(1)F6 octahedra. The corner-sharing octahedral tilt angles range from 34-51°. The Fe(6)-F(2) bond length is 2.00 Å. The Fe(6)-F(6) bond length is 2.23 Å. Both Fe(6)-F(3) bond lengths are 2.03 Å. Both Fe(6)-F(5) bond lengths are 2.28 Å. In the seventh Fe site, Fe(7) is bonded in a 6-coordinate geometry to one O(5), two equivalent O(7), one F(8), and two equivalent F(6) atoms. The Fe(7)-O(5) bond length is 1.92 Å. Both Fe(7)-O(7) bond lengths are 1.89 Å. The Fe(7)-F(8) bond length is 2.40 Å. Both Fe(7)-F(6) bond lengths are 2.32 Å. In the eighth Fe site, Fe(8) is bonded in a 5-coordinate geometry to one O(8), two equivalent O(6), and two equivalent F(7) atoms. The Fe(8)-O(8) bond length is 1.82 Å. Both Fe(8)-O(6) bond lengths are 1.95 Å. Both Fe(8)-F(7) bond lengths are 2.23 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 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 distorted 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 T-shaped geometry to one Fe(5) and two equivalent Fe(3) atoms. In the second F site, F(2) is bonded in a 3-coordinate 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 distorted 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 rectangular see-saw-like geometry to one Mg(1), 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 Mg(1) and two equivalent Fe(8) atoms. In the eighth F site, F(8) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Mg(1) and one Fe(7) atom.