MgFe8(OF)8 crystallizes in the triclinic P1 space group. Mg(1) is bonded in a 5-coordinate geometry to one O(2), one O(5), one F(5), one F(7), and one F(8) atom. There are eight inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(3), one O(6), one O(8), one F(1), one F(2), and one F(8) atom to form distorted FeO3F3 octahedra that share corners with three equivalent Fe(5)O3F2 trigonal bipyramids, corners with three equivalent Fe(7)O3F2 trigonal bipyramids, and  an edgeedge with one Fe(4)O3F3 octahedra. In the second Fe site, Fe(2) is bonded in a 6-coordinate geometry to one O(1), one O(4), one O(8), one F(1), one F(4), and one F(6) atom. In the third Fe site, Fe(3) is bonded to one O(1), one O(2), one O(7), one F(3), one F(6), and one F(7) atom to form distorted FeO3F3 octahedra that share corners with three equivalent Fe(6)O3F2 square pyramids, corners with three equivalent Fe(8)O3F2 trigonal bipyramids, and  an edgeedge with one Fe(4)O3F3 octahedra. In the fourth Fe site, Fe(4) is bonded to one O(2), one O(3), one O(5), one F(5), one F(7), and one F(8) atom to form distorted FeO3F3 octahedra that share corners with three equivalent Fe(6)O3F2 square pyramids, corners with three equivalent Fe(7)O3F2 trigonal bipyramids,  an edgeedge with one Fe(1)O3F3 octahedra, and  an edgeedge with one Fe(3)O3F3 octahedra. In the fifth Fe site, Fe(5) is bonded to one O(4), one O(6), one O(8), one F(2), and one F(4) atom to form distorted FeO3F2 trigonal bipyramids that share corners with three equivalent Fe(1)O3F3 octahedra,  an edgeedge with one Fe(7)O3F2 trigonal bipyramid, and  an edgeedge with one Fe(8)O3F2 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 47-51°. In the sixth Fe site, Fe(6) is bonded to one O(2), one O(5), one O(7), one F(3), and one F(5) atom to form distorted FeO3F2 square pyramids that share corners with three equivalent Fe(3)O3F3 octahedra, corners with three equivalent Fe(4)O3F3 octahedra,  an edgeedge with one Fe(7)O3F2 trigonal bipyramid, and  an edgeedge with one Fe(8)O3F2 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 46-65°. In the seventh Fe site, Fe(7) is bonded to one O(3), one O(5), one O(6), one F(2), and one F(5) atom to form distorted FeO3F2 trigonal bipyramids that share corners with three equivalent Fe(1)O3F3 octahedra, corners with three equivalent Fe(4)O3F3 octahedra,  an edgeedge with one Fe(6)O3F2 square pyramid, and  an edgeedge with one Fe(5)O3F2 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 42-55°. In the eighth Fe site, Fe(8) is bonded to one O(1), one O(4), one O(7), one F(3), and one F(4) atom to form FeO3F2 trigonal bipyramids that share corners with three equivalent Fe(3)O3F3 octahedra,  an edgeedge with one Fe(6)O3F2 square pyramid, and  an edgeedge with one Fe(5)O3F2 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 38-53°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Fe(2), one Fe(3), and one Fe(8) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Fe(3), one Fe(4), and one Fe(6) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Fe(1), one Fe(4), and one Fe(7) atom. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Fe(2), one Fe(5), and one Fe(8) atom. In the fifth O site, O(5) is bonded in a distorted tetrahedral geometry to one Mg(1), one Fe(4), one Fe(6), and one Fe(7) atom. In the sixth O site, O(6) is bonded in a trigonal planar geometry to one Fe(1), one Fe(5), and one Fe(7) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Fe(3), one Fe(6), and one Fe(8) atom. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(2), and one Fe(5) atom. There are eight inequivalent F sites. In the first F site, F(1) is bonded in a water-like geometry to one Fe(1) and one Fe(2) atom. In the second F site, F(2) is bonded in a 3-coordinate geometry to one Fe(1), one Fe(5), and one Fe(7) atom. In the third F site, F(3) is bonded in a 3-coordinate geometry to one Fe(3), one Fe(6), and one Fe(8) atom. In the fourth F site, F(4) is bonded in a 3-coordinate geometry to one Fe(2), one Fe(5), and one Fe(8) atom. In the fifth F site, F(5) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Fe(4), one Fe(6), and one Fe(7) atom. In the sixth F site, F(6) is bonded in an L-shaped geometry to one Fe(2) and one Fe(3) atom. In the seventh F site, F(7) is bonded in a distorted T-shaped geometry to one Mg(1), one Fe(3), and one Fe(4) atom. In the eighth F site, F(8) is bonded in a T-shaped geometry to one Mg(1), one Fe(1), and one Fe(4) atom.
MgFe8(OF)8 crystallizes in the triclinic P1 space group. Mg(1) is bonded in a 5-coordinate geometry to one O(2), one O(5), one F(5), one F(7), and one F(8) atom. The Mg(1)-O(2) bond length is 2.09 Å. The Mg(1)-O(5) bond length is 1.96 Å. The Mg(1)-F(5) bond length is 1.96 Å. The Mg(1)-F(7) bond length is 1.96 Å. The Mg(1)-F(8) bond length is 2.16 Å. There are eight inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(3), one O(6), one O(8), one F(1), one F(2), and one F(8) atom to form distorted FeO3F3 octahedra that share corners with three equivalent Fe(5)O3F2 trigonal bipyramids, corners with three equivalent Fe(7)O3F2 trigonal bipyramids, and  an edgeedge with one Fe(4)O3F3 octahedra. The Fe(1)-O(3) bond length is 1.99 Å. The Fe(1)-O(6) bond length is 1.93 Å. The Fe(1)-O(8) bond length is 1.97 Å. The Fe(1)-F(1) bond length is 1.99 Å. The Fe(1)-F(2) bond length is 2.52 Å. The Fe(1)-F(8) bond length is 2.09 Å. In the second Fe site, Fe(2) is bonded in a 6-coordinate geometry to one O(1), one O(4), one O(8), one F(1), one F(4), and one F(6) atom. The Fe(2)-O(1) bond length is 1.97 Å. The Fe(2)-O(4) bond length is 1.93 Å. The Fe(2)-O(8) bond length is 2.00 Å. The Fe(2)-F(1) bond length is 2.01 Å. The Fe(2)-F(4) bond length is 2.55 Å. The Fe(2)-F(6) bond length is 1.98 Å. In the third Fe site, Fe(3) is bonded to one O(1), one O(2), one O(7), one F(3), one F(6), and one F(7) atom to form distorted FeO3F3 octahedra that share corners with three equivalent Fe(6)O3F2 square pyramids, corners with three equivalent Fe(8)O3F2 trigonal bipyramids, and  an edgeedge with one Fe(4)O3F3 octahedra. The Fe(3)-O(1) bond length is 1.96 Å. The Fe(3)-O(2) bond length is 1.94 Å. The Fe(3)-O(7) bond length is 1.93 Å. The Fe(3)-F(3) bond length is 2.46 Å. The Fe(3)-F(6) bond length is 2.04 Å. The Fe(3)-F(7) bond length is 2.31 Å. In the fourth Fe site, Fe(4) is bonded to one O(2), one O(3), one O(5), one F(5), one F(7), and one F(8) atom to form distorted FeO3F3 octahedra that share corners with three equivalent Fe(6)O3F2 square pyramids, corners with three equivalent Fe(7)O3F2 trigonal bipyramids,  an edgeedge with one Fe(1)O3F3 octahedra, and  an edgeedge with one Fe(3)O3F3 octahedra. The Fe(4)-O(2) bond length is 2.04 Å. The Fe(4)-O(3) bond length is 2.05 Å. The Fe(4)-O(5) bond length is 2.10 Å. The Fe(4)-F(5) bond length is 2.31 Å. The Fe(4)-F(7) bond length is 2.11 Å. The Fe(4)-F(8) bond length is 2.11 Å. In the fifth Fe site, Fe(5) is bonded to one O(4), one O(6), one O(8), one F(2), and one F(4) atom to form distorted FeO3F2 trigonal bipyramids that share corners with three equivalent Fe(1)O3F3 octahedra,  an edgeedge with one Fe(7)O3F2 trigonal bipyramid, and  an edgeedge with one Fe(8)O3F2 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 47-51°. The Fe(5)-O(4) bond length is 1.94 Å. The Fe(5)-O(6) bond length is 1.98 Å. The Fe(5)-O(8) bond length is 1.90 Å. The Fe(5)-F(2) bond length is 2.09 Å. The Fe(5)-F(4) bond length is 2.02 Å. In the sixth Fe site, Fe(6) is bonded to one O(2), one O(5), one O(7), one F(3), and one F(5) atom to form distorted FeO3F2 square pyramids that share corners with three equivalent Fe(3)O3F3 octahedra, corners with three equivalent Fe(4)O3F3 octahedra,  an edgeedge with one Fe(7)O3F2 trigonal bipyramid, and  an edgeedge with one Fe(8)O3F2 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 46-65°. The Fe(6)-O(2) bond length is 2.10 Å. The Fe(6)-O(5) bond length is 2.09 Å. The Fe(6)-O(7) bond length is 2.03 Å. The Fe(6)-F(3) bond length is 2.08 Å. The Fe(6)-F(5) bond length is 2.22 Å. In the seventh Fe site, Fe(7) is bonded to one O(3), one O(5), one O(6), one F(2), and one F(5) atom to form distorted FeO3F2 trigonal bipyramids that share corners with three equivalent Fe(1)O3F3 octahedra, corners with three equivalent Fe(4)O3F3 octahedra,  an edgeedge with one Fe(6)O3F2 square pyramid, and  an edgeedge with one Fe(5)O3F2 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 42-55°. The Fe(7)-O(3) bond length is 1.89 Å. The Fe(7)-O(5) bond length is 1.93 Å. The Fe(7)-O(6) bond length is 1.95 Å. The Fe(7)-F(2) bond length is 1.99 Å. The Fe(7)-F(5) bond length is 2.20 Å. In the eighth Fe site, Fe(8) is bonded to one O(1), one O(4), one O(7), one F(3), and one F(4) atom to form FeO3F2 trigonal bipyramids that share corners with three equivalent Fe(3)O3F3 octahedra,  an edgeedge with one Fe(6)O3F2 square pyramid, and  an edgeedge with one Fe(5)O3F2 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 38-53°. The Fe(8)-O(1) bond length is 1.92 Å. The Fe(8)-O(4) bond length is 1.97 Å. The Fe(8)-O(7) bond length is 1.94 Å. The Fe(8)-F(3) bond length is 2.03 Å. The Fe(8)-F(4) bond length is 2.05 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Fe(2), one Fe(3), and one Fe(8) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Fe(3), one Fe(4), and one Fe(6) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Fe(1), one Fe(4), and one Fe(7) atom. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Fe(2), one Fe(5), and one Fe(8) atom. In the fifth O site, O(5) is bonded in a distorted tetrahedral geometry to one Mg(1), one Fe(4), one Fe(6), and one Fe(7) atom. In the sixth O site, O(6) is bonded in a trigonal planar geometry to one Fe(1), one Fe(5), and one Fe(7) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Fe(3), one Fe(6), and one Fe(8) atom. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(2), and one Fe(5) atom. There are eight inequivalent F sites. In the first F site, F(1) is bonded in a water-like geometry to one Fe(1) and one Fe(2) atom. In the second F site, F(2) is bonded in a 3-coordinate geometry to one Fe(1), one Fe(5), and one Fe(7) atom. In the third F site, F(3) is bonded in a 3-coordinate geometry to one Fe(3), one Fe(6), and one Fe(8) atom. In the fourth F site, F(4) is bonded in a 3-coordinate geometry to one Fe(2), one Fe(5), and one Fe(8) atom. In the fifth F site, F(5) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Fe(4), one Fe(6), and one Fe(7) atom. In the sixth F site, F(6) is bonded in an L-shaped geometry to one Fe(2) and one Fe(3) atom. In the seventh F site, F(7) is bonded in a distorted T-shaped geometry to one Mg(1), one Fe(3), and one Fe(4) atom. In the eighth F site, F(8) is bonded in a T-shaped geometry to one Mg(1), one Fe(1), and one Fe(4) atom.