MgDy2V2O7 crystallizes in the monoclinic Cm space group. Mg(1) is bonded in a 5-coordinate geometry to one O(4), two equivalent O(1), and two equivalent O(5) atoms. Dy(1) is bonded to one O(2), one O(3), two equivalent O(1), and two equivalent O(5) atoms to form distorted DyO6 pentagonal pyramids that share corners with two equivalent V(1)O5 trigonal bipyramids, corners with two equivalent V(2)O5 trigonal bipyramids, edges with three equivalent Dy(1)O6 pentagonal pyramids,  an edgeedge with one V(1)O5 trigonal bipyramid, and  an edgeedge with one V(2)O5 trigonal bipyramid. There are two inequivalent V sites. In the first V site, V(1) is bonded to one O(2), one O(3), one O(4), and two equivalent O(1) atoms to form distorted VO5 trigonal bipyramids that share corners with four equivalent Dy(1)O6 pentagonal pyramids,  a cornercorner with one V(2)O5 trigonal bipyramid, edges with two equivalent Dy(1)O6 pentagonal pyramids, and  an edgeedge with one V(2)O5 trigonal bipyramid. In the second V site, V(2) is bonded to one O(2), one O(3), one O(4), and two equivalent O(5) atoms to form VO5 trigonal bipyramids that share corners with four equivalent Dy(1)O6 pentagonal pyramids,  a cornercorner with one V(1)O5 trigonal bipyramid, edges with two equivalent Dy(1)O6 pentagonal pyramids, and  an edgeedge with one V(1)O5 trigonal bipyramid. There are five inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), two equivalent Dy(1), and one V(1) atom to form distorted ODy2MgV tetrahedra that share corners with two equivalent O(1)Dy2MgV tetrahedra,  a cornercorner with one O(3)Dy2V2 trigonal pyramid, corners with three equivalent O(2)Dy2V2 trigonal pyramids,  an edgeedge with one O(1)Dy2MgV tetrahedra, and  an edgeedge with one O(3)Dy2V2 trigonal pyramid. In the second O site, O(2) is bonded to two equivalent Dy(1), one V(1), and one V(2) atom to form ODy2V2 trigonal pyramids that share corners with six equivalent O(1)Dy2MgV tetrahedra and edges with two equivalent O(3)Dy2V2 trigonal pyramids. In the third O site, O(3) is bonded to two equivalent Dy(1), one V(1), and one V(2) atom to form ODy2V2 trigonal pyramids that share corners with two equivalent O(1)Dy2MgV tetrahedra, edges with two equivalent O(1)Dy2MgV tetrahedra, and edges with two equivalent O(2)Dy2V2 trigonal pyramids. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Mg(1), one V(1), and one V(2) atom. In the fifth O site, O(5) is bonded in a distorted see-saw-like geometry to one Mg(1), two equivalent Dy(1), and one V(2) atom.
MgDy2V2O7 crystallizes in the monoclinic Cm space group. Mg(1) is bonded in a 5-coordinate geometry to one O(4), two equivalent O(1), and two equivalent O(5) atoms. The Mg(1)-O(4) bond length is 2.01 Å. Both Mg(1)-O(1) bond lengths are 2.04 Å. Both Mg(1)-O(5) bond lengths are 2.22 Å. Dy(1) is bonded to one O(2), one O(3), two equivalent O(1), and two equivalent O(5) atoms to form distorted DyO6 pentagonal pyramids that share corners with two equivalent V(1)O5 trigonal bipyramids, corners with two equivalent V(2)O5 trigonal bipyramids, edges with three equivalent Dy(1)O6 pentagonal pyramids,  an edgeedge with one V(1)O5 trigonal bipyramid, and  an edgeedge with one V(2)O5 trigonal bipyramid. The Dy(1)-O(2) bond length is 2.31 Å. The Dy(1)-O(3) bond length is 2.31 Å. There is one shorter (2.24 Å) and one longer (2.31 Å) Dy(1)-O(1) bond length. There is one shorter (2.28 Å) and one longer (2.32 Å) Dy(1)-O(5) bond length. There are two inequivalent V sites. In the first V site, V(1) is bonded to one O(2), one O(3), one O(4), and two equivalent O(1) atoms to form distorted VO5 trigonal bipyramids that share corners with four equivalent Dy(1)O6 pentagonal pyramids,  a cornercorner with one V(2)O5 trigonal bipyramid, edges with two equivalent Dy(1)O6 pentagonal pyramids, and  an edgeedge with one V(2)O5 trigonal bipyramid. The V(1)-O(2) bond length is 2.01 Å. The V(1)-O(3) bond length is 2.25 Å. The V(1)-O(4) bond length is 1.87 Å. Both V(1)-O(1) bond lengths are 2.02 Å. In the second V site, V(2) is bonded to one O(2), one O(3), one O(4), and two equivalent O(5) atoms to form VO5 trigonal bipyramids that share corners with four equivalent Dy(1)O6 pentagonal pyramids,  a cornercorner with one V(1)O5 trigonal bipyramid, edges with two equivalent Dy(1)O6 pentagonal pyramids, and  an edgeedge with one V(1)O5 trigonal bipyramid. The V(2)-O(2) bond length is 2.17 Å. The V(2)-O(3) bond length is 1.96 Å. The V(2)-O(4) bond length is 2.01 Å. Both V(2)-O(5) bond lengths are 1.96 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), two equivalent Dy(1), and one V(1) atom to form distorted ODy2MgV tetrahedra that share corners with two equivalent O(1)Dy2MgV tetrahedra,  a cornercorner with one O(3)Dy2V2 trigonal pyramid, corners with three equivalent O(2)Dy2V2 trigonal pyramids,  an edgeedge with one O(1)Dy2MgV tetrahedra, and  an edgeedge with one O(3)Dy2V2 trigonal pyramid. In the second O site, O(2) is bonded to two equivalent Dy(1), one V(1), and one V(2) atom to form ODy2V2 trigonal pyramids that share corners with six equivalent O(1)Dy2MgV tetrahedra and edges with two equivalent O(3)Dy2V2 trigonal pyramids. In the third O site, O(3) is bonded to two equivalent Dy(1), one V(1), and one V(2) atom to form ODy2V2 trigonal pyramids that share corners with two equivalent O(1)Dy2MgV tetrahedra, edges with two equivalent O(1)Dy2MgV tetrahedra, and edges with two equivalent O(2)Dy2V2 trigonal pyramids. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Mg(1), one V(1), and one V(2) atom. In the fifth O site, O(5) is bonded in a distorted see-saw-like geometry to one Mg(1), two equivalent Dy(1), and one V(2) atom.