MgV4O8 crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one O(4), two equivalent O(6), and two equivalent O(7) atoms to form MgO5 square pyramids that share corners with two equivalent V(2)O6 octahedra, corners with two equivalent V(3)O6 octahedra, corners with two equivalent V(4)O6 octahedra,  an edgeedge with one V(4)O6 octahedra, edges with two equivalent V(1)O6 octahedra, edges with two equivalent Mg(1)O5 square pyramids, and  a faceface with one V(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 5-56°. There are four inequivalent V sites. In the first V site, V(1) is bonded to one O(2), one O(7), two equivalent O(4), and two equivalent O(5) atoms to form distorted VO6 octahedra that share corners with two equivalent V(2)O6 octahedra, corners with two equivalent V(3)O6 octahedra, edges with two equivalent V(1)O6 octahedra, edges with two equivalent V(4)O6 octahedra, and edges with two equivalent Mg(1)O5 square pyramids. The corner-sharing octahedral tilt angles range from 48-50°. In the second V site, V(2) is bonded to one O(4), one O(8), two equivalent O(3), and two equivalent O(6) atoms to form distorted VO6 octahedra that share corners with two equivalent V(1)O6 octahedra, corners with two equivalent V(4)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, edges with two equivalent V(2)O6 octahedra, edges with two equivalent V(3)O6 octahedra, and  a faceface with one Mg(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 48-53°. In the third V site, V(3) is bonded to one O(1), one O(6), two equivalent O(2), and two equivalent O(8) atoms to form VO6 octahedra that share corners with two equivalent V(1)O6 octahedra, corners with two equivalent V(4)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, edges with two equivalent V(2)O6 octahedra, and edges with two equivalent V(3)O6 octahedra. The corner-sharing octahedral tilt angles are 50°. In the fourth V site, V(4) is bonded to one O(3), one O(5), two equivalent O(1), and two equivalent O(7) atoms to form VO6 octahedra that share corners with two equivalent V(2)O6 octahedra, corners with two equivalent V(3)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, edges with two equivalent V(1)O6 octahedra, edges with two equivalent V(4)O6 octahedra, and  an edgeedge with one Mg(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 50-53°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one V(3) and two equivalent V(4) atoms. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one V(1) and two equivalent V(3) atoms. In the third O site, O(3) is bonded in a trigonal planar geometry to one V(4) and two equivalent V(2) atoms. In the fourth O site, O(4) is bonded to one Mg(1), one V(2), and two equivalent V(1) atoms to form OMgV3 trigonal pyramids that share corners with two equivalent O(4)MgV3 trigonal pyramids, edges with two equivalent O(7)Mg2V3 square pyramids, and edges with two equivalent O(6)Mg2V3 trigonal bipyramids. In the fifth O site, O(5) is bonded in a trigonal non-coplanar geometry to one V(4) and two equivalent V(1) atoms. In the sixth O site, O(6) is bonded to two equivalent Mg(1), one V(3), and two equivalent V(2) atoms to form distorted OMg2V3 trigonal bipyramids that share corners with two equivalent O(7)Mg2V3 square pyramids,  an edgeedge with one O(7)Mg2V3 square pyramid, edges with two equivalent O(6)Mg2V3 trigonal bipyramids, and edges with two equivalent O(4)MgV3 trigonal pyramids. In the seventh O site, O(7) is bonded to two equivalent Mg(1), one V(1), and two equivalent V(4) atoms to form OMg2V3 square pyramids that share corners with two equivalent O(6)Mg2V3 trigonal bipyramids, edges with two equivalent O(7)Mg2V3 square pyramids,  an edgeedge with one O(6)Mg2V3 trigonal bipyramid, and edges with two equivalent O(4)MgV3 trigonal pyramids. In the eighth O site, O(8) is bonded in a trigonal non-coplanar geometry to one V(2) and two equivalent V(3) atoms.
MgV4O8 crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one O(4), two equivalent O(6), and two equivalent O(7) atoms to form MgO5 square pyramids that share corners with two equivalent V(2)O6 octahedra, corners with two equivalent V(3)O6 octahedra, corners with two equivalent V(4)O6 octahedra,  an edgeedge with one V(4)O6 octahedra, edges with two equivalent V(1)O6 octahedra, edges with two equivalent Mg(1)O5 square pyramids, and  a faceface with one V(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 5-56°. The Mg(1)-O(4) bond length is 2.07 Å. Both Mg(1)-O(6) bond lengths are 2.11 Å. Both Mg(1)-O(7) bond lengths are 2.05 Å. There are four inequivalent V sites. In the first V site, V(1) is bonded to one O(2), one O(7), two equivalent O(4), and two equivalent O(5) atoms to form distorted VO6 octahedra that share corners with two equivalent V(2)O6 octahedra, corners with two equivalent V(3)O6 octahedra, edges with two equivalent V(1)O6 octahedra, edges with two equivalent V(4)O6 octahedra, and edges with two equivalent Mg(1)O5 square pyramids. The corner-sharing octahedral tilt angles range from 48-50°. The V(1)-O(2) bond length is 1.80 Å. The V(1)-O(7) bond length is 2.30 Å. Both V(1)-O(4) bond lengths are 2.04 Å. Both V(1)-O(5) bond lengths are 1.95 Å. In the second V site, V(2) is bonded to one O(4), one O(8), two equivalent O(3), and two equivalent O(6) atoms to form distorted VO6 octahedra that share corners with two equivalent V(1)O6 octahedra, corners with two equivalent V(4)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, edges with two equivalent V(2)O6 octahedra, edges with two equivalent V(3)O6 octahedra, and  a faceface with one Mg(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 48-53°. The V(2)-O(4) bond length is 1.99 Å. The V(2)-O(8) bond length is 1.80 Å. Both V(2)-O(3) bond lengths are 1.92 Å. Both V(2)-O(6) bond lengths are 2.20 Å. In the third V site, V(3) is bonded to one O(1), one O(6), two equivalent O(2), and two equivalent O(8) atoms to form VO6 octahedra that share corners with two equivalent V(1)O6 octahedra, corners with two equivalent V(4)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, edges with two equivalent V(2)O6 octahedra, and edges with two equivalent V(3)O6 octahedra. The corner-sharing octahedral tilt angles are 50°. The V(3)-O(1) bond length is 1.91 Å. The V(3)-O(6) bond length is 2.10 Å. Both V(3)-O(2) bond lengths are 2.06 Å. Both V(3)-O(8) bond lengths are 2.05 Å. In the fourth V site, V(4) is bonded to one O(3), one O(5), two equivalent O(1), and two equivalent O(7) atoms to form VO6 octahedra that share corners with two equivalent V(2)O6 octahedra, corners with two equivalent V(3)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, edges with two equivalent V(1)O6 octahedra, edges with two equivalent V(4)O6 octahedra, and  an edgeedge with one Mg(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 50-53°. The V(4)-O(3) bond length is 2.04 Å. The V(4)-O(5) bond length is 2.03 Å. Both V(4)-O(1) bond lengths are 1.97 Å. Both V(4)-O(7) bond lengths are 2.17 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one V(3) and two equivalent V(4) atoms. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one V(1) and two equivalent V(3) atoms. In the third O site, O(3) is bonded in a trigonal planar geometry to one V(4) and two equivalent V(2) atoms. In the fourth O site, O(4) is bonded to one Mg(1), one V(2), and two equivalent V(1) atoms to form OMgV3 trigonal pyramids that share corners with two equivalent O(4)MgV3 trigonal pyramids, edges with two equivalent O(7)Mg2V3 square pyramids, and edges with two equivalent O(6)Mg2V3 trigonal bipyramids. In the fifth O site, O(5) is bonded in a trigonal non-coplanar geometry to one V(4) and two equivalent V(1) atoms. In the sixth O site, O(6) is bonded to two equivalent Mg(1), one V(3), and two equivalent V(2) atoms to form distorted OMg2V3 trigonal bipyramids that share corners with two equivalent O(7)Mg2V3 square pyramids,  an edgeedge with one O(7)Mg2V3 square pyramid, edges with two equivalent O(6)Mg2V3 trigonal bipyramids, and edges with two equivalent O(4)MgV3 trigonal pyramids. In the seventh O site, O(7) is bonded to two equivalent Mg(1), one V(1), and two equivalent V(4) atoms to form OMg2V3 square pyramids that share corners with two equivalent O(6)Mg2V3 trigonal bipyramids, edges with two equivalent O(7)Mg2V3 square pyramids,  an edgeedge with one O(6)Mg2V3 trigonal bipyramid, and edges with two equivalent O(4)MgV3 trigonal pyramids. In the eighth O site, O(8) is bonded in a trigonal non-coplanar geometry to one V(2) and two equivalent V(3) atoms.