MgTb5(MoO6)2 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to two equivalent O(4) and four equivalent O(2) atoms to form MgO6 octahedra that share corners with four equivalent Mo(1)O6 octahedra and edges with two equivalent Tb(3)O6 octahedra. The corner-sharing octahedral tilt angles are 43°. There are three inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 7-coordinate geometry to one O(4), two equivalent O(1), and four equivalent O(2) atoms. In the second Tb site, Tb(2) is bonded in a 7-coordinate geometry to one O(4), two equivalent O(2), and four equivalent O(1) atoms. In the third Tb site, Tb(3) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form TbO6 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 49°. Mo(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form MoO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Tb(3)O6 octahedra, and edges with two equivalent Mo(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-49°. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Tb(1), two equivalent Tb(2), and one Mo(1) atom to form OTb3Mo tetrahedra that share corners with four equivalent O(1)Tb3Mo tetrahedra,  a cornercorner with one O(4)Tb2MgMo2 trigonal bipyramid, corners with six equivalent O(2)Tb4Mg trigonal bipyramids, edges with two equivalent O(1)Tb3Mo tetrahedra,  an edgeedge with one O(2)Tb4Mg trigonal bipyramid, and edges with two equivalent O(4)Tb2MgMo2 trigonal bipyramids. In the second O site, O(2) is bonded to one Mg(1), one Tb(2), one Tb(3), and two equivalent Tb(1) atoms to form OTb4Mg trigonal bipyramids that share corners with six equivalent O(1)Tb3Mo tetrahedra,  a cornercorner with one O(4)Tb2MgMo2 trigonal bipyramid, corners with four equivalent O(2)Tb4Mg trigonal bipyramids,  an edgeedge with one O(1)Tb3Mo tetrahedra, edges with two equivalent O(4)Tb2MgMo2 trigonal bipyramids, edges with three equivalent O(2)Tb4Mg trigonal bipyramids, and  a faceface with one O(2)Tb4Mg trigonal bipyramid. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Tb(3) and two equivalent Mo(1) atoms. In the fourth O site, O(4) is bonded to one Mg(1), one Tb(1), one Tb(2), and two equivalent Mo(1) atoms to form distorted OTb2MgMo2 trigonal bipyramids that share corners with two equivalent O(1)Tb3Mo tetrahedra,  a cornercorner with one O(4)Tb2MgMo2 trigonal bipyramid, corners with two equivalent O(2)Tb4Mg trigonal bipyramids, edges with four equivalent O(1)Tb3Mo tetrahedra,  an edgeedge with one O(4)Tb2MgMo2 trigonal bipyramid, and edges with four equivalent O(2)Tb4Mg trigonal bipyramids.
MgTb5(MoO6)2 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to two equivalent O(4) and four equivalent O(2) atoms to form MgO6 octahedra that share corners with four equivalent Mo(1)O6 octahedra and edges with two equivalent Tb(3)O6 octahedra. The corner-sharing octahedral tilt angles are 43°. Both Mg(1)-O(4) bond lengths are 2.07 Å. All Mg(1)-O(2) bond lengths are 2.20 Å. There are three inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 7-coordinate geometry to one O(4), two equivalent O(1), and four equivalent O(2) atoms. The Tb(1)-O(4) bond length is 2.61 Å. Both Tb(1)-O(1) bond lengths are 2.26 Å. There are two shorter (2.40 Å) and two longer (2.43 Å) Tb(1)-O(2) bond lengths. In the second Tb site, Tb(2) is bonded in a 7-coordinate geometry to one O(4), two equivalent O(2), and four equivalent O(1) atoms. The Tb(2)-O(4) bond length is 2.43 Å. Both Tb(2)-O(2) bond lengths are 2.52 Å. There are two shorter (2.22 Å) and two longer (2.36 Å) Tb(2)-O(1) bond lengths. In the third Tb site, Tb(3) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form TbO6 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 49°. Both Tb(3)-O(3) bond lengths are 2.27 Å. All Tb(3)-O(2) bond lengths are 2.33 Å. Mo(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form MoO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Tb(3)O6 octahedra, and edges with two equivalent Mo(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-49°. Both Mo(1)-O(1) bond lengths are 2.12 Å. Both Mo(1)-O(3) bond lengths are 2.07 Å. Both Mo(1)-O(4) bond lengths are 2.17 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Tb(1), two equivalent Tb(2), and one Mo(1) atom to form OTb3Mo tetrahedra that share corners with four equivalent O(1)Tb3Mo tetrahedra,  a cornercorner with one O(4)Tb2MgMo2 trigonal bipyramid, corners with six equivalent O(2)Tb4Mg trigonal bipyramids, edges with two equivalent O(1)Tb3Mo tetrahedra,  an edgeedge with one O(2)Tb4Mg trigonal bipyramid, and edges with two equivalent O(4)Tb2MgMo2 trigonal bipyramids. In the second O site, O(2) is bonded to one Mg(1), one Tb(2), one Tb(3), and two equivalent Tb(1) atoms to form OTb4Mg trigonal bipyramids that share corners with six equivalent O(1)Tb3Mo tetrahedra,  a cornercorner with one O(4)Tb2MgMo2 trigonal bipyramid, corners with four equivalent O(2)Tb4Mg trigonal bipyramids,  an edgeedge with one O(1)Tb3Mo tetrahedra, edges with two equivalent O(4)Tb2MgMo2 trigonal bipyramids, edges with three equivalent O(2)Tb4Mg trigonal bipyramids, and  a faceface with one O(2)Tb4Mg trigonal bipyramid. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Tb(3) and two equivalent Mo(1) atoms. In the fourth O site, O(4) is bonded to one Mg(1), one Tb(1), one Tb(2), and two equivalent Mo(1) atoms to form distorted OTb2MgMo2 trigonal bipyramids that share corners with two equivalent O(1)Tb3Mo tetrahedra,  a cornercorner with one O(4)Tb2MgMo2 trigonal bipyramid, corners with two equivalent O(2)Tb4Mg trigonal bipyramids, edges with four equivalent O(1)Tb3Mo tetrahedra,  an edgeedge with one O(4)Tb2MgMo2 trigonal bipyramid, and edges with four equivalent O(2)Tb4Mg trigonal bipyramids.