Mg5Tb9Ni4 crystallizes in the tetragonal P4/mmm space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 9-coordinate geometry to one Mg(1), four equivalent Tb(1), and four equivalent Tb(2) atoms. In the second Mg site, Mg(2) is bonded in a body-centered cubic geometry to eight equivalent Tb(1) atoms. There are three inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a distorted L-shaped geometry to two equivalent Mg(2), four equivalent Mg(1), and two equivalent Ni(1) atoms. In the second Tb site, Tb(2) is bonded in a 4-coordinate geometry to four equivalent Mg(1) and four equivalent Ni(1) atoms. In the third Tb site, Tb(3) is bonded in a square co-planar geometry to four equivalent Ni(1) atoms. Ni(1) is bonded in a 7-coordinate geometry to one Tb(3), two equivalent Tb(1), and four equivalent Tb(2) atoms.
Mg5Tb9Ni4 crystallizes in the tetragonal P4/mmm space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 9-coordinate geometry to one Mg(1), four equivalent Tb(1), and four equivalent Tb(2) atoms. The Mg(1)-Mg(1) bond length is 3.08 Å. All Mg(1)-Tb(1) bond lengths are 3.32 Å. All Mg(1)-Tb(2) bond lengths are 3.42 Å. In the second Mg site, Mg(2) is bonded in a body-centered cubic geometry to eight equivalent Tb(1) atoms. All Mg(2)-Tb(1) bond lengths are 3.31 Å. There are three inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a distorted L-shaped geometry to two equivalent Mg(2), four equivalent Mg(1), and two equivalent Ni(1) atoms. Both Tb(1)-Ni(1) bond lengths are 2.71 Å. In the second Tb site, Tb(2) is bonded in a 4-coordinate geometry to four equivalent Mg(1) and four equivalent Ni(1) atoms. All Tb(2)-Ni(1) bond lengths are 2.92 Å. In the third Tb site, Tb(3) is bonded in a square co-planar geometry to four equivalent Ni(1) atoms. All Tb(3)-Ni(1) bond lengths are 2.94 Å. Ni(1) is bonded in a 7-coordinate geometry to one Tb(3), two equivalent Tb(1), and four equivalent Tb(2) atoms.