Tb4Mg3Co2 crystallizes in the monoclinic P2/m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 10-coordinate geometry to one Mg(1), four equivalent Tb(1), four equivalent Tb(2), and one Co(1) atom. In the second Mg site, Mg(2) is bonded in a 10-coordinate geometry to four equivalent Tb(1), four equivalent Tb(2), and two equivalent Co(1) 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(2), four equivalent Mg(1), and four equivalent Co(1) atoms. In the second Tb site, Tb(2) is bonded in a distorted L-shaped geometry to two equivalent Mg(2), four equivalent Mg(1), and two equivalent Co(1) atoms. Co(1) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(2), two equivalent Tb(2), four equivalent Tb(1), and one Co(1) atom.
Tb4Mg3Co2 crystallizes in the monoclinic P2/m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 10-coordinate geometry to one Mg(1), four equivalent Tb(1), four equivalent Tb(2), and one Co(1) atom. The Mg(1)-Mg(1) bond length is 3.12 Å. There are two shorter (3.45 Å) and two longer (3.54 Å) Mg(1)-Tb(1) bond lengths. There are two shorter (3.30 Å) and two longer (3.45 Å) Mg(1)-Tb(2) bond lengths. The Mg(1)-Co(1) bond length is 3.21 Å. In the second Mg site, Mg(2) is bonded in a 10-coordinate geometry to four equivalent Tb(1), four equivalent Tb(2), and two equivalent Co(1) atoms. All Mg(2)-Tb(1) bond lengths are 3.39 Å. All Mg(2)-Tb(2) bond lengths are 3.20 Å. Both Mg(2)-Co(1) bond lengths are 3.06 Å. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 4-coordinate geometry to two equivalent Mg(2), four equivalent Mg(1), and four equivalent Co(1) atoms. There are two shorter (2.86 Å) and two longer (2.89 Å) Tb(1)-Co(1) bond lengths. In the second Tb site, Tb(2) is bonded in a distorted L-shaped geometry to two equivalent Mg(2), four equivalent Mg(1), and two equivalent Co(1) atoms. Both Tb(2)-Co(1) bond lengths are 2.71 Å. Co(1) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(2), two equivalent Tb(2), four equivalent Tb(1), and one Co(1) atom. The Co(1)-Co(1) bond length is 2.33 Å.