MgV3FeO8 crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one O(6), one O(7), one O(8), and two equivalent O(3) atoms to form MgO5 trigonal bipyramids that share corners with two equivalent Mg(1)O5 trigonal bipyramids,  an edgeedge with one V(3)O6 octahedra, edges with two equivalent V(1)O6 octahedra, and edges with two equivalent V(2)O6 octahedra. There are three inequivalent V sites. In the first V site, V(1) is bonded to one O(1), one O(2), one O(3), one O(4), and two equivalent O(7) atoms to form VO6 octahedra that share  a cornercorner with one V(2)O6 octahedra,  a cornercorner with one V(3)O6 octahedra, corners with two equivalent V(1)O6 octahedra,  an edgeedge with one V(2)O6 octahedra, edges with two equivalent V(3)O6 octahedra, and edges with two equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 5-18°. In the second V site, V(2) is bonded to one O(2), one O(3), one O(4), one O(5), and two equivalent O(8) atoms to form distorted VO6 octahedra that share  a cornercorner with one V(1)O6 octahedra, corners with two equivalent V(2)O6 octahedra,  an edgeedge with one V(1)O6 octahedra,  an edgeedge with one V(3)O6 octahedra, and edges with two equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 5-25°. In the third V site, V(3) is bonded to one O(4), one O(5), one O(6), one O(7), and two equivalent O(1) atoms to form VO6 octahedra that share  a cornercorner with one V(1)O6 octahedra, corners with two equivalent V(3)O6 octahedra,  an edgeedge with one V(2)O6 octahedra, edges with two equivalent V(1)O6 octahedra, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 18-28°. Fe(1) is bonded in a 6-coordinate geometry to one O(5), one O(6), one O(7), one O(8), and two equivalent O(2) atoms. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to one V(1) and two equivalent V(3) atoms. In the second O site, O(2) is bonded to one V(1), one V(2), and two equivalent Fe(1) atoms to form OV2Fe2 trigonal pyramids that share corners with two equivalent O(2)V2Fe2 trigonal pyramids and edges with two equivalent O(7)MgV3Fe square pyramids. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to two equivalent Mg(1), one V(1), and one V(2) atom. In the fourth O site, O(4) is bonded in a distorted T-shaped geometry to one V(1), one V(2), and one V(3) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one V(2), one V(3), and one Fe(1) atom. In the sixth O site, O(6) is bonded in a T-shaped geometry to one Mg(1), one V(3), and one Fe(1) atom. In the seventh O site, O(7) is bonded to one Mg(1), one V(3), two equivalent V(1), and one Fe(1) atom to form distorted OMgV3Fe square pyramids that share corners with two equivalent O(7)MgV3Fe square pyramids and edges with two equivalent O(2)V2Fe2 trigonal pyramids. In the eighth O site, O(8) is bonded in a rectangular see-saw-like geometry to one Mg(1), two equivalent V(2), and one Fe(1) atom.
MgV3FeO8 crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one O(6), one O(7), one O(8), and two equivalent O(3) atoms to form MgO5 trigonal bipyramids that share corners with two equivalent Mg(1)O5 trigonal bipyramids,  an edgeedge with one V(3)O6 octahedra, edges with two equivalent V(1)O6 octahedra, and edges with two equivalent V(2)O6 octahedra. The Mg(1)-O(6) bond length is 2.06 Å. The Mg(1)-O(7) bond length is 2.01 Å. The Mg(1)-O(8) bond length is 1.99 Å. Both Mg(1)-O(3) bond lengths are 2.01 Å. There are three inequivalent V sites. In the first V site, V(1) is bonded to one O(1), one O(2), one O(3), one O(4), and two equivalent O(7) atoms to form VO6 octahedra that share  a cornercorner with one V(2)O6 octahedra,  a cornercorner with one V(3)O6 octahedra, corners with two equivalent V(1)O6 octahedra,  an edgeedge with one V(2)O6 octahedra, edges with two equivalent V(3)O6 octahedra, and edges with two equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 5-18°. The V(1)-O(1) bond length is 1.93 Å. The V(1)-O(2) bond length is 2.00 Å. The V(1)-O(3) bond length is 2.27 Å. The V(1)-O(4) bond length is 1.81 Å. Both V(1)-O(7) bond lengths are 1.98 Å. In the second V site, V(2) is bonded to one O(2), one O(3), one O(4), one O(5), and two equivalent O(8) atoms to form distorted VO6 octahedra that share  a cornercorner with one V(1)O6 octahedra, corners with two equivalent V(2)O6 octahedra,  an edgeedge with one V(1)O6 octahedra,  an edgeedge with one V(3)O6 octahedra, and edges with two equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 5-25°. The V(2)-O(2) bond length is 2.11 Å. The V(2)-O(3) bond length is 1.97 Å. The V(2)-O(4) bond length is 2.13 Å. The V(2)-O(5) bond length is 1.79 Å. Both V(2)-O(8) bond lengths are 2.01 Å. In the third V site, V(3) is bonded to one O(4), one O(5), one O(6), one O(7), and two equivalent O(1) atoms to form VO6 octahedra that share  a cornercorner with one V(1)O6 octahedra, corners with two equivalent V(3)O6 octahedra,  an edgeedge with one V(2)O6 octahedra, edges with two equivalent V(1)O6 octahedra, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 18-28°. The V(3)-O(4) bond length is 2.00 Å. The V(3)-O(5) bond length is 2.13 Å. The V(3)-O(6) bond length is 1.95 Å. The V(3)-O(7) bond length is 2.13 Å. Both V(3)-O(1) bond lengths are 2.02 Å. Fe(1) is bonded in a 6-coordinate geometry to one O(5), one O(6), one O(7), one O(8), and two equivalent O(2) atoms. The Fe(1)-O(5) bond length is 1.98 Å. The Fe(1)-O(6) bond length is 1.84 Å. The Fe(1)-O(7) bond length is 2.64 Å. The Fe(1)-O(8) bond length is 2.12 Å. Both Fe(1)-O(2) bond lengths are 2.07 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to one V(1) and two equivalent V(3) atoms. In the second O site, O(2) is bonded to one V(1), one V(2), and two equivalent Fe(1) atoms to form OV2Fe2 trigonal pyramids that share corners with two equivalent O(2)V2Fe2 trigonal pyramids and edges with two equivalent O(7)MgV3Fe square pyramids. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to two equivalent Mg(1), one V(1), and one V(2) atom. In the fourth O site, O(4) is bonded in a distorted T-shaped geometry to one V(1), one V(2), and one V(3) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one V(2), one V(3), and one Fe(1) atom. In the sixth O site, O(6) is bonded in a T-shaped geometry to one Mg(1), one V(3), and one Fe(1) atom. In the seventh O site, O(7) is bonded to one Mg(1), one V(3), two equivalent V(1), and one Fe(1) atom to form distorted OMgV3Fe square pyramids that share corners with two equivalent O(7)MgV3Fe square pyramids and edges with two equivalent O(2)V2Fe2 trigonal pyramids. In the eighth O site, O(8) is bonded in a rectangular see-saw-like geometry to one Mg(1), two equivalent V(2), and one Fe(1) atom.