TbAl3 crystallizes in the trigonal R-3m space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded to three equivalent Al(2) and nine equivalent Al(1) atoms to form a mixture of distorted corner and face-sharing TbAl12 cuboctahedra. In the second Tb site, Tb(2) is bonded to six equivalent Al(1) and six equivalent Al(2) atoms to form a mixture of corner and face-sharing TbAl12 cuboctahedra. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded in a 10-coordinate geometry to one Tb(2), three equivalent Tb(1), two equivalent Al(2), and four equivalent Al(1) atoms. In the second Al site, Al(2) is bonded in a 12-coordinate geometry to two equivalent Tb(1), two equivalent Tb(2), four equivalent Al(1), and four equivalent Al(2) atoms.
TbAl3 crystallizes in the trigonal R-3m space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded to three equivalent Al(2) and nine equivalent Al(1) atoms to form a mixture of distorted corner and face-sharing TbAl12 cuboctahedra. All Tb(1)-Al(2) bond lengths are 3.02 Å. There are three shorter (3.02 Å) and six longer (3.11 Å) Tb(1)-Al(1) bond lengths. In the second Tb site, Tb(2) is bonded to six equivalent Al(1) and six equivalent Al(2) atoms to form a mixture of corner and face-sharing TbAl12 cuboctahedra. All Tb(2)-Al(1) bond lengths are 3.08 Å. All Tb(2)-Al(2) bond lengths are 3.10 Å. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded in a 10-coordinate geometry to one Tb(2), three equivalent Tb(1), two equivalent Al(2), and four equivalent Al(1) atoms. Both Al(1)-Al(2) bond lengths are 2.86 Å. There are two shorter (2.69 Å) and two longer (2.83 Å) Al(1)-Al(1) bond lengths. In the second Al site, Al(2) is bonded in a 12-coordinate geometry to two equivalent Tb(1), two equivalent Tb(2), four equivalent Al(1), and four equivalent Al(2) atoms. All Al(2)-Al(2) bond lengths are 3.10 Å.