MgY2V2O8 crystallizes in the monoclinic C2 space group. Mg(1) is bonded to two equivalent O(1) and two equivalent O(3) atoms to form MgO4 tetrahedra that share corners with two equivalent V(2)O6 octahedra, corners with two equivalent Y(2)O6 pentagonal pyramids, and  an edgeedge with one V(1)O6 octahedra. The corner-sharing octahedral tilt angles are 52°. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms. In the second Y site, Y(2) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted YO6 pentagonal pyramids that share corners with two equivalent V(2)O6 octahedra, corners with two equivalent Mg(1)O4 tetrahedra, edges with two equivalent V(1)O6 octahedra, and edges with two equivalent V(2)O6 octahedra. The corner-sharing octahedral tilt angles are 37°. There are two inequivalent V sites. In the first V site, V(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form VO6 octahedra that share edges with two equivalent V(2)O6 octahedra, edges with two equivalent Y(2)O6 pentagonal pyramids, and  an edgeedge with one Mg(1)O4 tetrahedra. In the second V site, V(2) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted VO6 octahedra that share corners with two equivalent Y(2)O6 pentagonal pyramids, corners with two equivalent Mg(1)O4 tetrahedra, edges with two equivalent V(1)O6 octahedra, and edges with two equivalent Y(2)O6 pentagonal pyramids. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to one Mg(1), one Y(1), and one V(1) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Y(1), one Y(2), one V(1), and one V(2) atom. In the third O site, O(3) is bonded in a trigonal non-coplanar geometry to one Mg(1), one Y(2), and one V(2) atom. In the fourth O site, O(4) is bonded to one Y(1), one Y(2), one V(1), and one V(2) atom to form distorted corner-sharing OY2V2 trigonal pyramids.
MgY2V2O8 crystallizes in the monoclinic C2 space group. Mg(1) is bonded to two equivalent O(1) and two equivalent O(3) atoms to form MgO4 tetrahedra that share corners with two equivalent V(2)O6 octahedra, corners with two equivalent Y(2)O6 pentagonal pyramids, and  an edgeedge with one V(1)O6 octahedra. The corner-sharing octahedral tilt angles are 52°. Both Mg(1)-O(1) bond lengths are 1.97 Å. Both Mg(1)-O(3) bond lengths are 2.00 Å. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms. Both Y(1)-O(1) bond lengths are 2.20 Å. Both Y(1)-O(2) bond lengths are 2.45 Å. Both Y(1)-O(4) bond lengths are 2.26 Å. In the second Y site, Y(2) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted YO6 pentagonal pyramids that share corners with two equivalent V(2)O6 octahedra, corners with two equivalent Mg(1)O4 tetrahedra, edges with two equivalent V(1)O6 octahedra, and edges with two equivalent V(2)O6 octahedra. The corner-sharing octahedral tilt angles are 37°. Both Y(2)-O(2) bond lengths are 2.23 Å. Both Y(2)-O(3) bond lengths are 2.23 Å. Both Y(2)-O(4) bond lengths are 2.32 Å. There are two inequivalent V sites. In the first V site, V(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form VO6 octahedra that share edges with two equivalent V(2)O6 octahedra, edges with two equivalent Y(2)O6 pentagonal pyramids, and  an edgeedge with one Mg(1)O4 tetrahedra. Both V(1)-O(1) bond lengths are 1.90 Å. Both V(1)-O(2) bond lengths are 2.17 Å. Both V(1)-O(4) bond lengths are 1.91 Å. In the second V site, V(2) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted VO6 octahedra that share corners with two equivalent Y(2)O6 pentagonal pyramids, corners with two equivalent Mg(1)O4 tetrahedra, edges with two equivalent V(1)O6 octahedra, and edges with two equivalent Y(2)O6 pentagonal pyramids. Both V(2)-O(2) bond lengths are 1.93 Å. Both V(2)-O(3) bond lengths are 1.88 Å. Both V(2)-O(4) bond lengths are 2.27 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to one Mg(1), one Y(1), and one V(1) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Y(1), one Y(2), one V(1), and one V(2) atom. In the third O site, O(3) is bonded in a trigonal non-coplanar geometry to one Mg(1), one Y(2), and one V(2) atom. In the fourth O site, O(4) is bonded to one Y(1), one Y(2), one V(1), and one V(2) atom to form distorted corner-sharing OY2V2 trigonal pyramids.