MgY5(MoO6)2 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to two equivalent O(1) and four equivalent O(3) atoms to form MgO6 octahedra that share corners with four equivalent Mo(1)O6 octahedra and edges with two equivalent Y(1)O6 octahedra. The corner-sharing octahedral tilt angles are 48°. There are three inequivalent Y sites. In the first Y site, Y(1) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form YO6 octahedra that share corners with four equivalent Mo(1)O6 octahedra and edges with two equivalent Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles are 41°. In the second Y site, Y(2) is bonded in a 7-coordinate geometry to one O(1), two equivalent O(3), and four equivalent O(4) atoms. In the third Y site, Y(3) is bonded in a 7-coordinate geometry to one O(1), two equivalent O(4), and four equivalent O(3) atoms. Mo(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form distorted MoO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Y(1)O6 octahedra, and edges with two equivalent Mo(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 41-48°. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Y(2), one Y(3), and two equivalent Mo(1) atoms to form OY2MgMo2 trigonal bipyramids that share corners with two equivalent O(4)Y3Mo tetrahedra,  a cornercorner with one O(1)Y2MgMo2 trigonal bipyramid, corners with two equivalent O(3)Y4Mg trigonal bipyramids, edges with four equivalent O(4)Y3Mo tetrahedra,  an edgeedge with one O(1)Y2MgMo2 trigonal bipyramid, and edges with four equivalent O(3)Y4Mg trigonal bipyramids. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Y(1) and two equivalent Mo(1) atoms. In the third O site, O(3) is bonded to one Mg(1), one Y(1), one Y(2), and two equivalent Y(3) atoms to form OY4Mg trigonal bipyramids that share corners with six equivalent O(4)Y3Mo tetrahedra,  a cornercorner with one O(1)Y2MgMo2 trigonal bipyramid, corners with four equivalent O(3)Y4Mg trigonal bipyramids,  an edgeedge with one O(4)Y3Mo tetrahedra, edges with two equivalent O(1)Y2MgMo2 trigonal bipyramids, edges with three equivalent O(3)Y4Mg trigonal bipyramids, and  a faceface with one O(3)Y4Mg trigonal bipyramid. In the fourth O site, O(4) is bonded to one Y(3), two equivalent Y(2), and one Mo(1) atom to form OY3Mo tetrahedra that share corners with four equivalent O(4)Y3Mo tetrahedra,  a cornercorner with one O(1)Y2MgMo2 trigonal bipyramid, corners with six equivalent O(3)Y4Mg trigonal bipyramids, edges with two equivalent O(4)Y3Mo tetrahedra,  an edgeedge with one O(3)Y4Mg trigonal bipyramid, and edges with two equivalent O(1)Y2MgMo2 trigonal bipyramids.
MgY5(MoO6)2 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to two equivalent O(1) and four equivalent O(3) atoms to form MgO6 octahedra that share corners with four equivalent Mo(1)O6 octahedra and edges with two equivalent Y(1)O6 octahedra. The corner-sharing octahedral tilt angles are 48°. Both Mg(1)-O(1) bond lengths are 2.23 Å. All Mg(1)-O(3) bond lengths are 2.15 Å. There are three inequivalent Y sites. In the first Y site, Y(1) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form YO6 octahedra that share corners with four equivalent Mo(1)O6 octahedra and edges with two equivalent Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles are 41°. Both Y(1)-O(2) bond lengths are 2.18 Å. All Y(1)-O(3) bond lengths are 2.31 Å. In the second Y site, Y(2) is bonded in a 7-coordinate geometry to one O(1), two equivalent O(3), and four equivalent O(4) atoms. The Y(2)-O(1) bond length is 2.32 Å. Both Y(2)-O(3) bond lengths are 2.52 Å. There are two shorter (2.23 Å) and two longer (2.38 Å) Y(2)-O(4) bond lengths. In the third Y site, Y(3) is bonded in a 7-coordinate geometry to one O(1), two equivalent O(4), and four equivalent O(3) atoms. The Y(3)-O(1) bond length is 2.50 Å. Both Y(3)-O(4) bond lengths are 2.28 Å. There are two shorter (2.39 Å) and two longer (2.43 Å) Y(3)-O(3) bond lengths. Mo(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form distorted MoO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Y(1)O6 octahedra, and edges with two equivalent Mo(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 41-48°. Both Mo(1)-O(1) bond lengths are 2.27 Å. Both Mo(1)-O(2) bond lengths are 2.04 Å. Both Mo(1)-O(4) bond lengths are 2.07 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Y(2), one Y(3), and two equivalent Mo(1) atoms to form OY2MgMo2 trigonal bipyramids that share corners with two equivalent O(4)Y3Mo tetrahedra,  a cornercorner with one O(1)Y2MgMo2 trigonal bipyramid, corners with two equivalent O(3)Y4Mg trigonal bipyramids, edges with four equivalent O(4)Y3Mo tetrahedra,  an edgeedge with one O(1)Y2MgMo2 trigonal bipyramid, and edges with four equivalent O(3)Y4Mg trigonal bipyramids. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Y(1) and two equivalent Mo(1) atoms. In the third O site, O(3) is bonded to one Mg(1), one Y(1), one Y(2), and two equivalent Y(3) atoms to form OY4Mg trigonal bipyramids that share corners with six equivalent O(4)Y3Mo tetrahedra,  a cornercorner with one O(1)Y2MgMo2 trigonal bipyramid, corners with four equivalent O(3)Y4Mg trigonal bipyramids,  an edgeedge with one O(4)Y3Mo tetrahedra, edges with two equivalent O(1)Y2MgMo2 trigonal bipyramids, edges with three equivalent O(3)Y4Mg trigonal bipyramids, and  a faceface with one O(3)Y4Mg trigonal bipyramid. In the fourth O site, O(4) is bonded to one Y(3), two equivalent Y(2), and one Mo(1) atom to form OY3Mo tetrahedra that share corners with four equivalent O(4)Y3Mo tetrahedra,  a cornercorner with one O(1)Y2MgMo2 trigonal bipyramid, corners with six equivalent O(3)Y4Mg trigonal bipyramids, edges with two equivalent O(4)Y3Mo tetrahedra,  an edgeedge with one O(3)Y4Mg trigonal bipyramid, and edges with two equivalent O(1)Y2MgMo2 trigonal bipyramids.