MgV2Cd2O7 crystallizes in the monoclinic C2 space group. Mg(1) is bonded to one O(3), two equivalent O(1), and two equivalent O(2) atoms to form distorted MgO5 trigonal bipyramids that share corners with two equivalent V(1)O5 trigonal bipyramids, edges with two equivalent Cd(2)O6 octahedra, and edges with two equivalent V(1)O5 trigonal bipyramids. V(1) is bonded to one O(1), one O(2), one O(3), and two equivalent O(4) atoms to form VO5 trigonal bipyramids that share corners with two equivalent Cd(2)O6 octahedra,  a cornercorner with one Mg(1)O5 trigonal bipyramid,  a cornercorner with one V(1)O5 trigonal bipyramid,  an edgeedge with one Cd(2)O6 octahedra,  an edgeedge with one Mg(1)O5 trigonal bipyramid, and  an edgeedge with one V(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 19-55°. There are two inequivalent Cd sites. In the first Cd site, Cd(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 Cd site, Cd(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form distorted CdO6 octahedra that share corners with four equivalent V(1)O5 trigonal bipyramids, edges with two equivalent Mg(1)O5 trigonal bipyramids, and edges with two equivalent V(1)O5 trigonal bipyramids. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one V(1), one Cd(1), and one Cd(2) atom to form distorted OMgVCd2 trigonal pyramids that share corners with three equivalent O(1)MgVCd2 trigonal pyramids, corners with four equivalent O(4)V2Cd2 trigonal pyramids, and  an edgeedge with one O(4)V2Cd2 trigonal pyramid. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one V(1), one Cd(1), and one Cd(2) atom. In the third O site, O(3) is bonded in a T-shaped geometry to one Mg(1) and two equivalent V(1) atoms. In the fourth O site, O(4) is bonded to two equivalent V(1), one Cd(1), and one Cd(2) atom to form distorted OV2Cd2 trigonal pyramids that share corners with four equivalent O(1)MgVCd2 trigonal pyramids,  an edgeedge with one O(1)MgVCd2 trigonal pyramid, and edges with two equivalent O(4)V2Cd2 trigonal pyramids.
MgV2Cd2O7 crystallizes in the monoclinic C2 space group. Mg(1) is bonded to one O(3), two equivalent O(1), and two equivalent O(2) atoms to form distorted MgO5 trigonal bipyramids that share corners with two equivalent V(1)O5 trigonal bipyramids, edges with two equivalent Cd(2)O6 octahedra, and edges with two equivalent V(1)O5 trigonal bipyramids. The Mg(1)-O(3) bond length is 2.07 Å. Both Mg(1)-O(1) bond lengths are 2.06 Å. Both Mg(1)-O(2) bond lengths are 2.14 Å. V(1) is bonded to one O(1), one O(2), one O(3), and two equivalent O(4) atoms to form VO5 trigonal bipyramids that share corners with two equivalent Cd(2)O6 octahedra,  a cornercorner with one Mg(1)O5 trigonal bipyramid,  a cornercorner with one V(1)O5 trigonal bipyramid,  an edgeedge with one Cd(2)O6 octahedra,  an edgeedge with one Mg(1)O5 trigonal bipyramid, and  an edgeedge with one V(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 19-55°. The V(1)-O(1) bond length is 1.92 Å. The V(1)-O(2) bond length is 1.79 Å. The V(1)-O(3) bond length is 1.91 Å. There is one shorter (1.87 Å) and one longer (2.10 Å) V(1)-O(4) bond length. There are two inequivalent Cd sites. In the first Cd site, Cd(1) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms. Both Cd(1)-O(1) bond lengths are 2.27 Å. Both Cd(1)-O(2) bond lengths are 2.63 Å. Both Cd(1)-O(4) bond lengths are 2.37 Å. In the second Cd site, Cd(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form distorted CdO6 octahedra that share corners with four equivalent V(1)O5 trigonal bipyramids, edges with two equivalent Mg(1)O5 trigonal bipyramids, and edges with two equivalent V(1)O5 trigonal bipyramids. Both Cd(2)-O(1) bond lengths are 2.32 Å. Both Cd(2)-O(2) bond lengths are 2.32 Å. Both Cd(2)-O(4) bond lengths are 2.30 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one V(1), one Cd(1), and one Cd(2) atom to form distorted OMgVCd2 trigonal pyramids that share corners with three equivalent O(1)MgVCd2 trigonal pyramids, corners with four equivalent O(4)V2Cd2 trigonal pyramids, and  an edgeedge with one O(4)V2Cd2 trigonal pyramid. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one V(1), one Cd(1), and one Cd(2) atom. In the third O site, O(3) is bonded in a T-shaped geometry to one Mg(1) and two equivalent V(1) atoms. In the fourth O site, O(4) is bonded to two equivalent V(1), one Cd(1), and one Cd(2) atom to form distorted OV2Cd2 trigonal pyramids that share corners with four equivalent O(1)MgVCd2 trigonal pyramids,  an edgeedge with one O(1)MgVCd2 trigonal pyramid, and edges with two equivalent O(4)V2Cd2 trigonal pyramids.