MgTb4(WO6)2 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(10), one O(12), one O(2), one O(6), and one O(8) atom to form distorted MgO5 trigonal bipyramids that share  a cornercorner with one Tb(3)O7 pentagonal bipyramid and edges with two equivalent W(2)O6 octahedra. There are four inequivalent Tb sites. In the first Tb site, Tb(1) is bonded to one O(1), one O(11), one O(3), one O(4), one O(5), one O(7), and one O(9) atom to form distorted TbO7 pentagonal bipyramids that share corners with two equivalent Tb(3)O7 pentagonal bipyramids,  an edgeedge with one W(2)O6 octahedra, and edges with two equivalent Tb(3)O7 pentagonal bipyramids. In the second Tb site, Tb(2) is bonded in a 7-coordinate geometry to one O(11), one O(12), one O(2), one O(3), one O(4), one O(6), and one O(9) atom. In the third Tb site, Tb(3) is bonded to one O(1), one O(10), one O(11), one O(3), one O(4), one O(7), and one O(9) atom to form distorted TbO7 pentagonal bipyramids that share corners with two equivalent W(2)O6 octahedra, corners with two equivalent Tb(1)O7 pentagonal bipyramids,  a cornercorner with one Mg(1)O5 trigonal bipyramid, and edges with two equivalent Tb(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 34-54°. In the fourth Tb site, Tb(4) is bonded in a 7-coordinate geometry to one O(11), one O(12), one O(3), one O(4), one O(6), one O(8), and one O(9) atom. There are two inequivalent W sites. In the first W site, W(1) is bonded in a 5-coordinate geometry to one O(1), one O(10), one O(12), one O(2), and one O(5) atom. In the second W site, W(2) is bonded to one O(10), one O(2), one O(5), one O(6), one O(7), and one O(8) atom to form WO6 octahedra that share corners with two equivalent Tb(3)O7 pentagonal bipyramids,  an edgeedge with one Tb(1)O7 pentagonal bipyramid, and edges with two equivalent Mg(1)O5 trigonal bipyramids. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Tb(1), one Tb(3), and one W(1) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Tb(2), one W(1), and one W(2) atom. In the third O site, O(3) is bonded to one Tb(1), one Tb(2), one Tb(3), and one Tb(4) atom to form OTb4 tetrahedra that share corners with four equivalent O(4)Tb4 tetrahedra,  a cornercorner with one O(10)TbMgW2 trigonal pyramid, corners with two equivalent O(6)Tb2MgW trigonal pyramids, edges with two equivalent O(11)Tb4 tetrahedra, and edges with two equivalent O(9)Tb4 tetrahedra. In the fourth O site, O(4) is bonded to one Tb(1), one Tb(2), one Tb(3), and one Tb(4) atom to form OTb4 tetrahedra that share corners with four equivalent O(3)Tb4 tetrahedra,  a cornercorner with one O(10)TbMgW2 trigonal pyramid, corners with two equivalent O(6)Tb2MgW trigonal pyramids, edges with two equivalent O(11)Tb4 tetrahedra, and edges with two equivalent O(9)Tb4 tetrahedra. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Tb(1), one W(1), and one W(2) atom. In the sixth O site, O(6) is bonded to one Mg(1), one Tb(2), one Tb(4), and one W(2) atom to form distorted OTb2MgW trigonal pyramids that share corners with two equivalent O(11)Tb4 tetrahedra, corners with two equivalent O(3)Tb4 tetrahedra, corners with two equivalent O(4)Tb4 tetrahedra,  an edgeedge with one O(9)Tb4 tetrahedra, and  an edgeedge with one O(10)TbMgW2 trigonal pyramid. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Tb(1), one Tb(3), and one W(2) atom. In the eighth O site, O(8) is bonded in a distorted trigonal non-coplanar geometry to one Mg(1), one Tb(4), and one W(2) atom. In the ninth O site, O(9) is bonded to one Tb(1), one Tb(2), one Tb(3), and one Tb(4) atom to form OTb4 tetrahedra that share corners with four equivalent O(11)Tb4 tetrahedra,  a cornercorner with one O(10)TbMgW2 trigonal pyramid, edges with two equivalent O(3)Tb4 tetrahedra, edges with two equivalent O(4)Tb4 tetrahedra, and  an edgeedge with one O(6)Tb2MgW trigonal pyramid. In the tenth O site, O(10) is bonded to one Mg(1), one Tb(3), one W(1), and one W(2) atom to form distorted OTbMgW2 trigonal pyramids that share  a cornercorner with one O(11)Tb4 tetrahedra,  a cornercorner with one O(3)Tb4 tetrahedra,  a cornercorner with one O(4)Tb4 tetrahedra,  a cornercorner with one O(9)Tb4 tetrahedra, and  an edgeedge with one O(6)Tb2MgW trigonal pyramid. In the eleventh O site, O(11) is bonded to one Tb(1), one Tb(2), one Tb(3), and one Tb(4) atom to form OTb4 tetrahedra that share corners with four equivalent O(9)Tb4 tetrahedra,  a cornercorner with one O(10)TbMgW2 trigonal pyramid, corners with two equivalent O(6)Tb2MgW trigonal pyramids, edges with two equivalent O(3)Tb4 tetrahedra, and edges with two equivalent O(4)Tb4 tetrahedra. In the twelfth O site, O(12) is bonded in a 4-coordinate geometry to one Mg(1), one Tb(2), one Tb(4), and one W(1) atom.
MgTb4(WO6)2 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(10), one O(12), one O(2), one O(6), and one O(8) atom to form distorted MgO5 trigonal bipyramids that share  a cornercorner with one Tb(3)O7 pentagonal bipyramid and edges with two equivalent W(2)O6 octahedra. The Mg(1)-O(10) bond length is 2.08 Å. The Mg(1)-O(12) bond length is 2.09 Å. The Mg(1)-O(2) bond length is 2.00 Å. The Mg(1)-O(6) bond length is 2.00 Å. The Mg(1)-O(8) bond length is 1.98 Å. There are four inequivalent Tb sites. In the first Tb site, Tb(1) is bonded to one O(1), one O(11), one O(3), one O(4), one O(5), one O(7), and one O(9) atom to form distorted TbO7 pentagonal bipyramids that share corners with two equivalent Tb(3)O7 pentagonal bipyramids,  an edgeedge with one W(2)O6 octahedra, and edges with two equivalent Tb(3)O7 pentagonal bipyramids. The Tb(1)-O(1) bond length is 2.36 Å. The Tb(1)-O(11) bond length is 2.32 Å. The Tb(1)-O(3) bond length is 2.28 Å. The Tb(1)-O(4) bond length is 2.34 Å. The Tb(1)-O(5) bond length is 2.45 Å. The Tb(1)-O(7) bond length is 2.45 Å. The Tb(1)-O(9) bond length is 2.25 Å. In the second Tb site, Tb(2) is bonded in a 7-coordinate geometry to one O(11), one O(12), one O(2), one O(3), one O(4), one O(6), and one O(9) atom. The Tb(2)-O(11) bond length is 2.24 Å. The Tb(2)-O(12) bond length is 2.36 Å. The Tb(2)-O(2) bond length is 2.78 Å. The Tb(2)-O(3) bond length is 2.21 Å. The Tb(2)-O(4) bond length is 2.24 Å. The Tb(2)-O(6) bond length is 2.51 Å. The Tb(2)-O(9) bond length is 2.31 Å. In the third Tb site, Tb(3) is bonded to one O(1), one O(10), one O(11), one O(3), one O(4), one O(7), and one O(9) atom to form distorted TbO7 pentagonal bipyramids that share corners with two equivalent W(2)O6 octahedra, corners with two equivalent Tb(1)O7 pentagonal bipyramids,  a cornercorner with one Mg(1)O5 trigonal bipyramid, and edges with two equivalent Tb(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 34-54°. The Tb(3)-O(1) bond length is 2.47 Å. The Tb(3)-O(10) bond length is 2.56 Å. The Tb(3)-O(11) bond length is 2.28 Å. The Tb(3)-O(3) bond length is 2.29 Å. The Tb(3)-O(4) bond length is 2.38 Å. The Tb(3)-O(7) bond length is 2.36 Å. The Tb(3)-O(9) bond length is 2.25 Å. In the fourth Tb site, Tb(4) is bonded in a 7-coordinate geometry to one O(11), one O(12), one O(3), one O(4), one O(6), one O(8), and one O(9) atom. The Tb(4)-O(11) bond length is 2.27 Å. The Tb(4)-O(12) bond length is 2.67 Å. The Tb(4)-O(3) bond length is 2.30 Å. The Tb(4)-O(4) bond length is 2.24 Å. The Tb(4)-O(6) bond length is 2.48 Å. The Tb(4)-O(8) bond length is 2.42 Å. The Tb(4)-O(9) bond length is 2.30 Å. There are two inequivalent W sites. In the first W site, W(1) is bonded in a 5-coordinate geometry to one O(1), one O(10), one O(12), one O(2), and one O(5) atom. The W(1)-O(1) bond length is 1.85 Å. The W(1)-O(10) bond length is 2.23 Å. The W(1)-O(12) bond length is 1.94 Å. The W(1)-O(2) bond length is 2.03 Å. The W(1)-O(5) bond length is 1.95 Å. In the second W site, W(2) is bonded to one O(10), one O(2), one O(5), one O(6), one O(7), and one O(8) atom to form WO6 octahedra that share corners with two equivalent Tb(3)O7 pentagonal bipyramids,  an edgeedge with one Tb(1)O7 pentagonal bipyramid, and edges with two equivalent Mg(1)O5 trigonal bipyramids. The W(2)-O(10) bond length is 2.09 Å. The W(2)-O(2) bond length is 2.25 Å. The W(2)-O(5) bond length is 2.16 Å. The W(2)-O(6) bond length is 1.99 Å. The W(2)-O(7) bond length is 1.86 Å. The W(2)-O(8) bond length is 1.99 Å. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Tb(1), one Tb(3), and one W(1) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Tb(2), one W(1), and one W(2) atom. In the third O site, O(3) is bonded to one Tb(1), one Tb(2), one Tb(3), and one Tb(4) atom to form OTb4 tetrahedra that share corners with four equivalent O(4)Tb4 tetrahedra,  a cornercorner with one O(10)TbMgW2 trigonal pyramid, corners with two equivalent O(6)Tb2MgW trigonal pyramids, edges with two equivalent O(11)Tb4 tetrahedra, and edges with two equivalent O(9)Tb4 tetrahedra. In the fourth O site, O(4) is bonded to one Tb(1), one Tb(2), one Tb(3), and one Tb(4) atom to form OTb4 tetrahedra that share corners with four equivalent O(3)Tb4 tetrahedra,  a cornercorner with one O(10)TbMgW2 trigonal pyramid, corners with two equivalent O(6)Tb2MgW trigonal pyramids, edges with two equivalent O(11)Tb4 tetrahedra, and edges with two equivalent O(9)Tb4 tetrahedra. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Tb(1), one W(1), and one W(2) atom. In the sixth O site, O(6) is bonded to one Mg(1), one Tb(2), one Tb(4), and one W(2) atom to form distorted OTb2MgW trigonal pyramids that share corners with two equivalent O(11)Tb4 tetrahedra, corners with two equivalent O(3)Tb4 tetrahedra, corners with two equivalent O(4)Tb4 tetrahedra,  an edgeedge with one O(9)Tb4 tetrahedra, and  an edgeedge with one O(10)TbMgW2 trigonal pyramid. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Tb(1), one Tb(3), and one W(2) atom. In the eighth O site, O(8) is bonded in a distorted trigonal non-coplanar geometry to one Mg(1), one Tb(4), and one W(2) atom. In the ninth O site, O(9) is bonded to one Tb(1), one Tb(2), one Tb(3), and one Tb(4) atom to form OTb4 tetrahedra that share corners with four equivalent O(11)Tb4 tetrahedra,  a cornercorner with one O(10)TbMgW2 trigonal pyramid, edges with two equivalent O(3)Tb4 tetrahedra, edges with two equivalent O(4)Tb4 tetrahedra, and  an edgeedge with one O(6)Tb2MgW trigonal pyramid. In the tenth O site, O(10) is bonded to one Mg(1), one Tb(3), one W(1), and one W(2) atom to form distorted OTbMgW2 trigonal pyramids that share  a cornercorner with one O(11)Tb4 tetrahedra,  a cornercorner with one O(3)Tb4 tetrahedra,  a cornercorner with one O(4)Tb4 tetrahedra,  a cornercorner with one O(9)Tb4 tetrahedra, and  an edgeedge with one O(6)Tb2MgW trigonal pyramid. In the eleventh O site, O(11) is bonded to one Tb(1), one Tb(2), one Tb(3), and one Tb(4) atom to form OTb4 tetrahedra that share corners with four equivalent O(9)Tb4 tetrahedra,  a cornercorner with one O(10)TbMgW2 trigonal pyramid, corners with two equivalent O(6)Tb2MgW trigonal pyramids, edges with two equivalent O(3)Tb4 tetrahedra, and edges with two equivalent O(4)Tb4 tetrahedra. In the twelfth O site, O(12) is bonded in a 4-coordinate geometry to one Mg(1), one Tb(2), one Tb(4), and one W(1) atom.