MgTb2Cu(GeO3)4 crystallizes in the triclinic P1 space group. Mg(1) is bonded in a 5-coordinate geometry to one O(1), one O(11), one O(5), one O(7), and one O(9) atom. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 7-coordinate geometry to one O(1), one O(10), one O(2), one O(3), one O(4), one O(5), and one O(9) atom. In the second Tb site, Tb(2) is bonded to one O(1), one O(11), one O(2), one O(3), one O(4), one O(6), and one O(8) atom to form distorted TbO7 pentagonal bipyramids that share corners with two equivalent Ge(2)O4 tetrahedra, corners with two equivalent Ge(4)O4 tetrahedra, and  an edgeedge with one Ge(3)O4 tetrahedra. Cu(1) is bonded in a distorted T-shaped geometry to one O(10), one O(11), and one O(8) atom. There are four inequivalent Ge sites. In the first Ge site, Ge(1) is bonded in a rectangular see-saw-like geometry to one O(1), one O(11), one O(5), and one O(7) atom. In the second Ge site, Ge(2) is bonded to one O(10), one O(12), one O(2), and one O(6) atom to form GeO4 tetrahedra that share corners with two equivalent Tb(2)O7 pentagonal bipyramids,  a cornercorner with one Ge(3)O4 tetrahedra, and  a cornercorner with one Ge(4)O4 tetrahedra. In the third Ge site, Ge(3) is bonded to one O(3), one O(6), one O(7), and one O(9) atom to form GeO4 tetrahedra that share  a cornercorner with one Ge(2)O4 tetrahedra and  an edgeedge with one Tb(2)O7 pentagonal bipyramid. In the fourth Ge site, Ge(4) is bonded to one O(12), one O(4), one O(5), and one O(8) atom to form GeO4 tetrahedra that share corners with two equivalent Tb(2)O7 pentagonal bipyramids and  a cornercorner with one Ge(2)O4 tetrahedra. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a distorted tetrahedral geometry to one Mg(1), one Tb(1), one Tb(2), and one Ge(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Tb(1), one Tb(2), and one Ge(2) atom. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Tb(1), one Tb(2), and one Ge(3) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Tb(1), one Tb(2), and one Ge(4) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Mg(1), one Tb(1), one Ge(1), and one Ge(4) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Tb(2), one Ge(2), and one Ge(3) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Mg(1), one Ge(1), and one Ge(3) atom. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Tb(2), one Cu(1), and one Ge(4) atom. In the ninth O site, O(9) is bonded in a trigonal planar geometry to one Mg(1), one Tb(1), and one Ge(3) atom. In the tenth O site, O(10) is bonded in a distorted trigonal planar geometry to one Tb(1), one Cu(1), and one Ge(2) atom. In the eleventh O site, O(11) is bonded in a distorted see-saw-like geometry to one Mg(1), one Tb(2), one Cu(1), and one Ge(1) atom. In the twelfth O site, O(12) is bonded in a distorted bent 120 degrees geometry to one Ge(2) and one Ge(4) atom.
MgTb2Cu(GeO3)4 crystallizes in the triclinic P1 space group. Mg(1) is bonded in a 5-coordinate geometry to one O(1), one O(11), one O(5), one O(7), and one O(9) atom. The Mg(1)-O(1) bond length is 2.24 Å. The Mg(1)-O(11) bond length is 2.07 Å. The Mg(1)-O(5) bond length is 2.14 Å. The Mg(1)-O(7) bond length is 2.04 Å. The Mg(1)-O(9) bond length is 2.12 Å. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 7-coordinate geometry to one O(1), one O(10), one O(2), one O(3), one O(4), one O(5), and one O(9) atom. The Tb(1)-O(1) bond length is 2.28 Å. The Tb(1)-O(10) bond length is 2.32 Å. The Tb(1)-O(2) bond length is 2.46 Å. The Tb(1)-O(3) bond length is 2.26 Å. The Tb(1)-O(4) bond length is 2.33 Å. The Tb(1)-O(5) bond length is 2.78 Å. The Tb(1)-O(9) bond length is 2.37 Å. In the second Tb site, Tb(2) is bonded to one O(1), one O(11), one O(2), one O(3), one O(4), one O(6), and one O(8) atom to form distorted TbO7 pentagonal bipyramids that share corners with two equivalent Ge(2)O4 tetrahedra, corners with two equivalent Ge(4)O4 tetrahedra, and  an edgeedge with one Ge(3)O4 tetrahedra. The Tb(2)-O(1) bond length is 2.55 Å. The Tb(2)-O(11) bond length is 2.32 Å. The Tb(2)-O(2) bond length is 2.39 Å. The Tb(2)-O(3) bond length is 2.42 Å. The Tb(2)-O(4) bond length is 2.27 Å. The Tb(2)-O(6) bond length is 2.48 Å. The Tb(2)-O(8) bond length is 2.24 Å. Cu(1) is bonded in a distorted T-shaped geometry to one O(10), one O(11), and one O(8) atom. The Cu(1)-O(10) bond length is 1.94 Å. The Cu(1)-O(11) bond length is 1.93 Å. The Cu(1)-O(8) bond length is 2.06 Å. There are four inequivalent Ge sites. In the first Ge site, Ge(1) is bonded in a rectangular see-saw-like geometry to one O(1), one O(11), one O(5), and one O(7) atom. The Ge(1)-O(1) bond length is 1.89 Å. The Ge(1)-O(11) bond length is 2.08 Å. The Ge(1)-O(5) bond length is 1.95 Å. The Ge(1)-O(7) bond length is 1.97 Å. In the second Ge site, Ge(2) is bonded to one O(10), one O(12), one O(2), and one O(6) atom to form GeO4 tetrahedra that share corners with two equivalent Tb(2)O7 pentagonal bipyramids,  a cornercorner with one Ge(3)O4 tetrahedra, and  a cornercorner with one Ge(4)O4 tetrahedra. The Ge(2)-O(10) bond length is 1.76 Å. The Ge(2)-O(12) bond length is 1.81 Å. The Ge(2)-O(2) bond length is 1.76 Å. The Ge(2)-O(6) bond length is 1.81 Å. In the third Ge site, Ge(3) is bonded to one O(3), one O(6), one O(7), and one O(9) atom to form GeO4 tetrahedra that share  a cornercorner with one Ge(2)O4 tetrahedra and  an edgeedge with one Tb(2)O7 pentagonal bipyramid. The Ge(3)-O(3) bond length is 1.74 Å. The Ge(3)-O(6) bond length is 1.83 Å. The Ge(3)-O(7) bond length is 1.80 Å. The Ge(3)-O(9) bond length is 1.75 Å. In the fourth Ge site, Ge(4) is bonded to one O(12), one O(4), one O(5), and one O(8) atom to form GeO4 tetrahedra that share corners with two equivalent Tb(2)O7 pentagonal bipyramids and  a cornercorner with one Ge(2)O4 tetrahedra. The Ge(4)-O(12) bond length is 1.82 Å. The Ge(4)-O(4) bond length is 1.75 Å. The Ge(4)-O(5) bond length is 1.83 Å. The Ge(4)-O(8) bond length is 1.72 Å. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a distorted tetrahedral geometry to one Mg(1), one Tb(1), one Tb(2), and one Ge(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Tb(1), one Tb(2), and one Ge(2) atom. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Tb(1), one Tb(2), and one Ge(3) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Tb(1), one Tb(2), and one Ge(4) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Mg(1), one Tb(1), one Ge(1), and one Ge(4) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Tb(2), one Ge(2), and one Ge(3) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Mg(1), one Ge(1), and one Ge(3) atom. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Tb(2), one Cu(1), and one Ge(4) atom. In the ninth O site, O(9) is bonded in a trigonal planar geometry to one Mg(1), one Tb(1), and one Ge(3) atom. In the tenth O site, O(10) is bonded in a distorted trigonal planar geometry to one Tb(1), one Cu(1), and one Ge(2) atom. In the eleventh O site, O(11) is bonded in a distorted see-saw-like geometry to one Mg(1), one Tb(2), one Cu(1), and one Ge(1) atom. In the twelfth O site, O(12) is bonded in a distorted bent 120 degrees geometry to one Ge(2) and one Ge(4) atom.