MgFe10O9F11 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(1), one O(6), one F(10), one F(11), one F(4), and one F(6) atom to form MgO2F4 octahedra that share corners with two equivalent Fe(1)O2F4 octahedra, corners with two equivalent Fe(4)O2F4 octahedra, edges with two equivalent Fe(10)O3F3 octahedra, edges with two equivalent Fe(9)O3F3 octahedra, and faces with two equivalent Fe(5)O2F4 octahedra. The corner-sharing octahedral tilt angles range from 38-50°. There are ten inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(2), one O(7), one F(1), one F(10), one F(4), and one F(7) atom to form FeO2F4 octahedra that share corners with two equivalent Mg(1)O2F4 octahedra, corners with four equivalent Fe(10)O3F3 octahedra, corners with four equivalent Fe(6)O4F2 octahedra,  an edgeedge with one Fe(2)O2F4 octahedra, and  an edgeedge with one Fe(5)O2F4 octahedra. The corner-sharing octahedral tilt angles range from 38-63°. In the second Fe site, Fe(2) is bonded to one O(3), one O(8), one F(1), one F(2), one F(7), and one F(9) atom to form FeO2F4 octahedra that share corners with four equivalent Fe(6)O4F2 octahedra, corners with four equivalent Fe(8)O4F2 octahedra,  an edgeedge with one Fe(1)O2F4 octahedra, and  an edgeedge with one Fe(3)O2F4 octahedra. The corner-sharing octahedral tilt angles range from 47-50°. In the third Fe site, Fe(3) is bonded to one O(4), one O(9), one F(2), one F(3), one F(8), and one F(9) atom to form FeO2F4 octahedra that share corners with four equivalent Fe(7)O3F3 octahedra, corners with four equivalent Fe(8)O4F2 octahedra,  an edgeedge with one Fe(2)O2F4 octahedra, and  an edgeedge with one Fe(4)O2F4 octahedra. The corner-sharing octahedral tilt angles range from 45-52°. In the fourth Fe site, Fe(4) is bonded to one O(1), one O(5), one F(11), one F(3), one F(5), and one F(8) atom to form FeO2F4 octahedra that share corners with two equivalent Mg(1)O2F4 octahedra, corners with four equivalent Fe(7)O3F3 octahedra, corners with four equivalent Fe(9)O3F3 octahedra,  an edgeedge with one Fe(3)O2F4 octahedra, and  an edgeedge with one Fe(5)O2F4 octahedra. The corner-sharing octahedral tilt angles range from 44-57°. In the fifth Fe site, Fe(5) is bonded to one O(1), one O(6), one F(10), one F(11), one F(4), and one F(6) atom to form distorted FeO2F4 octahedra that share corners with four equivalent Fe(10)O3F3 octahedra, corners with four equivalent Fe(9)O3F3 octahedra,  an edgeedge with one Fe(1)O2F4 octahedra,  an edgeedge with one Fe(4)O2F4 octahedra, and faces with two equivalent Mg(1)O2F4 octahedra. The corner-sharing octahedral tilt angles range from 30-63°. In the sixth Fe site, Fe(6) is bonded to one O(2), one O(3), one O(7), one O(8), one F(1), and one F(7) atom to form FeO4F2 octahedra that share corners with four equivalent Fe(1)O2F4 octahedra, corners with four equivalent Fe(2)O2F4 octahedra,  an edgeedge with one Fe(10)O3F3 octahedra, and  an edgeedge with one Fe(8)O4F2 octahedra. The corner-sharing octahedral tilt angles range from 44-49°. In the seventh Fe site, Fe(7) is bonded to one O(4), one O(5), one O(9), one F(3), one F(5), and one F(8) atom to form FeO3F3 octahedra that share corners with four equivalent Fe(3)O2F4 octahedra, corners with four equivalent Fe(4)O2F4 octahedra,  an edgeedge with one Fe(9)O3F3 octahedra, and  an edgeedge with one Fe(8)O4F2 octahedra. The corner-sharing octahedral tilt angles range from 45-54°. In the eighth Fe site, Fe(8) is bonded to one O(3), one O(4), one O(8), one O(9), one F(2), and one F(9) atom to form FeO4F2 octahedra that share corners with four equivalent Fe(2)O2F4 octahedra, corners with four equivalent Fe(3)O2F4 octahedra,  an edgeedge with one Fe(7)O3F3 octahedra, and  an edgeedge with one Fe(6)O4F2 octahedra. The corner-sharing octahedral tilt angles range from 45-50°. In the ninth Fe site, Fe(9) is bonded to one O(1), one O(5), one O(6), one F(11), one F(5), and one F(6) atom to form distorted FeO3F3 octahedra that share corners with four equivalent Fe(4)O2F4 octahedra, corners with four equivalent Fe(5)O2F4 octahedra,  an edgeedge with one Fe(10)O3F3 octahedra,  an edgeedge with one Fe(7)O3F3 octahedra, and edges with two equivalent Mg(1)O2F4 octahedra. The corner-sharing octahedral tilt angles range from 30-63°. In the tenth Fe site, Fe(10) is bonded to one O(2), one O(6), one O(7), one F(10), one F(4), and one F(6) atom to form distorted FeO3F3 octahedra that share corners with four equivalent Fe(1)O2F4 octahedra, corners with four equivalent Fe(5)O2F4 octahedra,  an edgeedge with one Fe(9)O3F3 octahedra,  an edgeedge with one Fe(6)O4F2 octahedra, and edges with two equivalent Mg(1)O2F4 octahedra. The corner-sharing octahedral tilt angles range from 36-63°. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Fe(4), one Fe(5), and one Fe(9) atom. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Fe(1), one Fe(10), and one Fe(6) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Fe(2), one Fe(6), and one Fe(8) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Fe(3), one Fe(7), and one Fe(8) atom. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Fe(4), one Fe(7), and one Fe(9) atom. In the sixth O site, O(6) is bonded to one Mg(1), one Fe(10), one Fe(5), and one Fe(9) atom to form OMgFe3 trigonal pyramids that share corners with two equivalent F(6)MgFe3 trigonal pyramids and  an edgeedge with one F(6)MgFe3 trigonal pyramid. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(10), and one Fe(6) atom. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Fe(2), one Fe(6), and one Fe(8) atom. In the ninth O site, O(9) is bonded in a distorted trigonal planar geometry to one Fe(3), one Fe(7), and one Fe(8) atom. There are eleven inequivalent F sites. In the first F site, F(1) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(2), and one Fe(6) atom. In the second F site, F(2) is bonded in a distorted trigonal planar geometry to one Fe(2), one Fe(3), and one Fe(8) atom. In the third F site, F(3) is bonded in a distorted trigonal planar geometry to one Fe(3), one Fe(4), and one Fe(7) atom. In the fourth F site, F(4) is bonded in a 4-coordinate geometry to one Mg(1), one Fe(1), one Fe(10), and one Fe(5) atom. In the fifth F site, F(5) is bonded in a 3-coordinate geometry to one Fe(4), one Fe(7), and one Fe(9) atom. In the sixth F site, F(6) is bonded to one Mg(1), one Fe(10), one Fe(5), and one Fe(9) atom to form distorted FMgFe3 trigonal pyramids that share corners with two equivalent O(6)MgFe3 trigonal pyramids and  an edgeedge with one O(6)MgFe3 trigonal pyramid. In the seventh F site, F(7) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(2), and one Fe(6) atom. In the eighth F site, F(8) is bonded in a distorted T-shaped geometry to one Fe(3), one Fe(4), and one Fe(7) atom. In the ninth F site, F(9) is bonded in a distorted trigonal planar geometry to one Fe(2), one Fe(3), and one Fe(8) atom. In the tenth F site, F(10) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Fe(1), one Fe(10), and one Fe(5) atom. In the eleventh F site, F(11) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Fe(4), one Fe(5), and one Fe(9) atom.
MgFe10O9F11 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(1), one O(6), one F(10), one F(11), one F(4), and one F(6) atom to form MgO2F4 octahedra that share corners with two equivalent Fe(1)O2F4 octahedra, corners with two equivalent Fe(4)O2F4 octahedra, edges with two equivalent Fe(10)O3F3 octahedra, edges with two equivalent Fe(9)O3F3 octahedra, and faces with two equivalent Fe(5)O2F4 octahedra. The corner-sharing octahedral tilt angles range from 38-50°. The Mg(1)-O(1) bond length is 2.11 Å. The Mg(1)-O(6) bond length is 1.98 Å. The Mg(1)-F(10) bond length is 2.08 Å. The Mg(1)-F(11) bond length is 2.00 Å. The Mg(1)-F(4) bond length is 2.12 Å. The Mg(1)-F(6) bond length is 1.93 Å. There are ten inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(2), one O(7), one F(1), one F(10), one F(4), and one F(7) atom to form FeO2F4 octahedra that share corners with two equivalent Mg(1)O2F4 octahedra, corners with four equivalent Fe(10)O3F3 octahedra, corners with four equivalent Fe(6)O4F2 octahedra,  an edgeedge with one Fe(2)O2F4 octahedra, and  an edgeedge with one Fe(5)O2F4 octahedra. The corner-sharing octahedral tilt angles range from 38-63°. The Fe(1)-O(2) bond length is 1.89 Å. The Fe(1)-O(7) bond length is 1.93 Å. The Fe(1)-F(1) bond length is 2.10 Å. The Fe(1)-F(10) bond length is 2.24 Å. The Fe(1)-F(4) bond length is 2.16 Å. The Fe(1)-F(7) bond length is 2.09 Å. In the second Fe site, Fe(2) is bonded to one O(3), one O(8), one F(1), one F(2), one F(7), and one F(9) atom to form FeO2F4 octahedra that share corners with four equivalent Fe(6)O4F2 octahedra, corners with four equivalent Fe(8)O4F2 octahedra,  an edgeedge with one Fe(1)O2F4 octahedra, and  an edgeedge with one Fe(3)O2F4 octahedra. The corner-sharing octahedral tilt angles range from 47-50°. The Fe(2)-O(3) bond length is 1.96 Å. The Fe(2)-O(8) bond length is 1.97 Å. The Fe(2)-F(1) bond length is 2.05 Å. The Fe(2)-F(2) bond length is 2.06 Å. The Fe(2)-F(7) bond length is 2.05 Å. The Fe(2)-F(9) bond length is 2.05 Å. In the third Fe site, Fe(3) is bonded to one O(4), one O(9), one F(2), one F(3), one F(8), and one F(9) atom to form FeO2F4 octahedra that share corners with four equivalent Fe(7)O3F3 octahedra, corners with four equivalent Fe(8)O4F2 octahedra,  an edgeedge with one Fe(2)O2F4 octahedra, and  an edgeedge with one Fe(4)O2F4 octahedra. The corner-sharing octahedral tilt angles range from 45-52°. The Fe(3)-O(4) bond length is 1.97 Å. The Fe(3)-O(9) bond length is 1.95 Å. The Fe(3)-F(2) bond length is 2.09 Å. The Fe(3)-F(3) bond length is 2.03 Å. The Fe(3)-F(8) bond length is 2.03 Å. The Fe(3)-F(9) bond length is 2.07 Å. In the fourth Fe site, Fe(4) is bonded to one O(1), one O(5), one F(11), one F(3), one F(5), and one F(8) atom to form FeO2F4 octahedra that share corners with two equivalent Mg(1)O2F4 octahedra, corners with four equivalent Fe(7)O3F3 octahedra, corners with four equivalent Fe(9)O3F3 octahedra,  an edgeedge with one Fe(3)O2F4 octahedra, and  an edgeedge with one Fe(5)O2F4 octahedra. The corner-sharing octahedral tilt angles range from 44-57°. The Fe(4)-O(1) bond length is 2.09 Å. The Fe(4)-O(5) bond length is 1.98 Å. The Fe(4)-F(11) bond length is 2.46 Å. The Fe(4)-F(3) bond length is 2.18 Å. The Fe(4)-F(5) bond length is 2.06 Å. The Fe(4)-F(8) bond length is 2.25 Å. In the fifth Fe site, Fe(5) is bonded to one O(1), one O(6), one F(10), one F(11), one F(4), and one F(6) atom to form distorted FeO2F4 octahedra that share corners with four equivalent Fe(10)O3F3 octahedra, corners with four equivalent Fe(9)O3F3 octahedra,  an edgeedge with one Fe(1)O2F4 octahedra,  an edgeedge with one Fe(4)O2F4 octahedra, and faces with two equivalent Mg(1)O2F4 octahedra. The corner-sharing octahedral tilt angles range from 30-63°. The Fe(5)-O(1) bond length is 2.01 Å. The Fe(5)-O(6) bond length is 1.96 Å. The Fe(5)-F(10) bond length is 2.21 Å. The Fe(5)-F(11) bond length is 2.23 Å. The Fe(5)-F(4) bond length is 2.12 Å. The Fe(5)-F(6) bond length is 2.11 Å. In the sixth Fe site, Fe(6) is bonded to one O(2), one O(3), one O(7), one O(8), one F(1), and one F(7) atom to form FeO4F2 octahedra that share corners with four equivalent Fe(1)O2F4 octahedra, corners with four equivalent Fe(2)O2F4 octahedra,  an edgeedge with one Fe(10)O3F3 octahedra, and  an edgeedge with one Fe(8)O4F2 octahedra. The corner-sharing octahedral tilt angles range from 44-49°. The Fe(6)-O(2) bond length is 2.01 Å. The Fe(6)-O(3) bond length is 2.01 Å. The Fe(6)-O(7) bond length is 2.02 Å. The Fe(6)-O(8) bond length is 2.01 Å. The Fe(6)-F(1) bond length is 2.24 Å. The Fe(6)-F(7) bond length is 2.25 Å. In the seventh Fe site, Fe(7) is bonded to one O(4), one O(5), one O(9), one F(3), one F(5), and one F(8) atom to form FeO3F3 octahedra that share corners with four equivalent Fe(3)O2F4 octahedra, corners with four equivalent Fe(4)O2F4 octahedra,  an edgeedge with one Fe(9)O3F3 octahedra, and  an edgeedge with one Fe(8)O4F2 octahedra. The corner-sharing octahedral tilt angles range from 45-54°. The Fe(7)-O(4) bond length is 1.92 Å. The Fe(7)-O(5) bond length is 1.94 Å. The Fe(7)-O(9) bond length is 1.95 Å. The Fe(7)-F(3) bond length is 2.21 Å. The Fe(7)-F(5) bond length is 2.28 Å. The Fe(7)-F(8) bond length is 2.18 Å. In the eighth Fe site, Fe(8) is bonded to one O(3), one O(4), one O(8), one O(9), one F(2), and one F(9) atom to form FeO4F2 octahedra that share corners with four equivalent Fe(2)O2F4 octahedra, corners with four equivalent Fe(3)O2F4 octahedra,  an edgeedge with one Fe(7)O3F3 octahedra, and  an edgeedge with one Fe(6)O4F2 octahedra. The corner-sharing octahedral tilt angles range from 45-50°. The Fe(8)-O(3) bond length is 1.98 Å. The Fe(8)-O(4) bond length is 2.02 Å. The Fe(8)-O(8) bond length is 1.97 Å. The Fe(8)-O(9) bond length is 2.03 Å. The Fe(8)-F(2) bond length is 2.25 Å. The Fe(8)-F(9) bond length is 2.28 Å. In the ninth Fe site, Fe(9) is bonded to one O(1), one O(5), one O(6), one F(11), one F(5), and one F(6) atom to form distorted FeO3F3 octahedra that share corners with four equivalent Fe(4)O2F4 octahedra, corners with four equivalent Fe(5)O2F4 octahedra,  an edgeedge with one Fe(10)O3F3 octahedra,  an edgeedge with one Fe(7)O3F3 octahedra, and edges with two equivalent Mg(1)O2F4 octahedra. The corner-sharing octahedral tilt angles range from 30-63°. The Fe(9)-O(1) bond length is 1.91 Å. The Fe(9)-O(5) bond length is 1.90 Å. The Fe(9)-O(6) bond length is 1.99 Å. The Fe(9)-F(11) bond length is 2.28 Å. The Fe(9)-F(5) bond length is 2.03 Å. The Fe(9)-F(6) bond length is 2.28 Å. In the tenth Fe site, Fe(10) is bonded to one O(2), one O(6), one O(7), one F(10), one F(4), and one F(6) atom to form distorted FeO3F3 octahedra that share corners with four equivalent Fe(1)O2F4 octahedra, corners with four equivalent Fe(5)O2F4 octahedra,  an edgeedge with one Fe(9)O3F3 octahedra,  an edgeedge with one Fe(6)O4F2 octahedra, and edges with two equivalent Mg(1)O2F4 octahedra. The corner-sharing octahedral tilt angles range from 36-63°. The Fe(10)-O(2) bond length is 2.04 Å. The Fe(10)-O(6) bond length is 2.04 Å. The Fe(10)-O(7) bond length is 2.00 Å. The Fe(10)-F(10) bond length is 2.28 Å. The Fe(10)-F(4) bond length is 2.30 Å. The Fe(10)-F(6) bond length is 2.44 Å. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Fe(4), one Fe(5), and one Fe(9) atom. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Fe(1), one Fe(10), and one Fe(6) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Fe(2), one Fe(6), and one Fe(8) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Fe(3), one Fe(7), and one Fe(8) atom. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Fe(4), one Fe(7), and one Fe(9) atom. In the sixth O site, O(6) is bonded to one Mg(1), one Fe(10), one Fe(5), and one Fe(9) atom to form OMgFe3 trigonal pyramids that share corners with two equivalent F(6)MgFe3 trigonal pyramids and  an edgeedge with one F(6)MgFe3 trigonal pyramid. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(10), and one Fe(6) atom. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Fe(2), one Fe(6), and one Fe(8) atom. In the ninth O site, O(9) is bonded in a distorted trigonal planar geometry to one Fe(3), one Fe(7), and one Fe(8) atom. There are eleven inequivalent F sites. In the first F site, F(1) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(2), and one Fe(6) atom. In the second F site, F(2) is bonded in a distorted trigonal planar geometry to one Fe(2), one Fe(3), and one Fe(8) atom. In the third F site, F(3) is bonded in a distorted trigonal planar geometry to one Fe(3), one Fe(4), and one Fe(7) atom. In the fourth F site, F(4) is bonded in a 4-coordinate geometry to one Mg(1), one Fe(1), one Fe(10), and one Fe(5) atom. In the fifth F site, F(5) is bonded in a 3-coordinate geometry to one Fe(4), one Fe(7), and one Fe(9) atom. In the sixth F site, F(6) is bonded to one Mg(1), one Fe(10), one Fe(5), and one Fe(9) atom to form distorted FMgFe3 trigonal pyramids that share corners with two equivalent O(6)MgFe3 trigonal pyramids and  an edgeedge with one O(6)MgFe3 trigonal pyramid. In the seventh F site, F(7) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(2), and one Fe(6) atom. In the eighth F site, F(8) is bonded in a distorted T-shaped geometry to one Fe(3), one Fe(4), and one Fe(7) atom. In the ninth F site, F(9) is bonded in a distorted trigonal planar geometry to one Fe(2), one Fe(3), and one Fe(8) atom. In the tenth F site, F(10) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Fe(1), one Fe(10), and one Fe(5) atom. In the eleventh F site, F(11) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Fe(4), one Fe(5), and one Fe(9) atom.