TbCuMg4 crystallizes in the orthorhombic Cmmm space group. There are six inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a distorted single-bond geometry to two equivalent Mg(2) and one Cu(1) atom. In the second Mg site, Mg(2) is bonded in a 11-coordinate geometry to one Mg(6), two equivalent Mg(4), four equivalent Mg(1), and four equivalent Mg(3) atoms. In the third Mg site, Mg(3) is bonded in a distorted single-bond geometry to two equivalent Mg(2), two equivalent Mg(6), and one Cu(1) atom. In the fourth Mg site, Mg(4) is bonded in an L-shaped geometry to one Mg(2) and two equivalent Cu(1) atoms. In the fifth Mg site, Mg(5) is bonded to four equivalent Tb(1), four equivalent Tb(2), and four equivalent Cu(1) atoms to form face-sharing MgTb8Cu4 cuboctahedra. In the sixth Mg site, Mg(6) is bonded in a 10-coordinate geometry to two equivalent Mg(2) and eight equivalent Mg(3) atoms. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 4-coordinate geometry to two equivalent Mg(5) and four equivalent Cu(1) atoms. In the second Tb site, Tb(2) is bonded in a 4-coordinate geometry to two equivalent Mg(5) and four equivalent Cu(1) atoms. Cu(1) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(3), one Mg(5), two equivalent Mg(4), two equivalent Tb(1), and two equivalent Tb(2) atoms.
TbCuMg4 crystallizes in the orthorhombic Cmmm space group. There are six inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a distorted single-bond geometry to two equivalent Mg(2) and one Cu(1) atom. Both Mg(1)-Mg(2) bond lengths are 3.11 Å. The Mg(1)-Cu(1) bond length is 2.85 Å. In the second Mg site, Mg(2) is bonded in a 11-coordinate geometry to one Mg(6), two equivalent Mg(4), four equivalent Mg(1), and four equivalent Mg(3) atoms. The Mg(2)-Mg(6) bond length is 3.32 Å. Both Mg(2)-Mg(4) bond lengths are 3.30 Å. All Mg(2)-Mg(3) bond lengths are 3.14 Å. In the third Mg site, Mg(3) is bonded in a distorted single-bond geometry to two equivalent Mg(2), two equivalent Mg(6), and one Cu(1) atom. Both Mg(3)-Mg(6) bond lengths are 3.08 Å. The Mg(3)-Cu(1) bond length is 2.87 Å. In the fourth Mg site, Mg(4) is bonded in an L-shaped geometry to one Mg(2) and two equivalent Cu(1) atoms. Both Mg(4)-Cu(1) bond lengths are 2.66 Å. In the fifth Mg site, Mg(5) is bonded to four equivalent Tb(1), four equivalent Tb(2), and four equivalent Cu(1) atoms to form face-sharing MgTb8Cu4 cuboctahedra. All Mg(5)-Tb(1) bond lengths are 3.30 Å. All Mg(5)-Tb(2) bond lengths are 3.30 Å. All Mg(5)-Cu(1) bond lengths are 3.01 Å. In the sixth Mg site, Mg(6) is bonded in a 10-coordinate geometry to two equivalent Mg(2) and eight equivalent Mg(3) atoms. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 4-coordinate geometry to two equivalent Mg(5) and four equivalent Cu(1) atoms. All Tb(1)-Cu(1) bond lengths are 2.92 Å. In the second Tb site, Tb(2) is bonded in a 4-coordinate geometry to two equivalent Mg(5) and four equivalent Cu(1) atoms. All Tb(2)-Cu(1) bond lengths are 2.94 Å. Cu(1) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(3), one Mg(5), two equivalent Mg(4), two equivalent Tb(1), and two equivalent Tb(2) atoms.