Tb2Al17 crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 18-coordinate geometry to six equivalent Al(3) and twelve equivalent Al(4) atoms. In the second Tb site, Tb(2) is bonded in a 20-coordinate geometry to two equivalent Al(1), six equivalent Al(2), six equivalent Al(3), and six equivalent Al(4) atoms. There are four inequivalent Al sites. In the first Al site, Al(1) is bonded in a 2-coordinate geometry to one Tb(2), one Al(1), three equivalent Al(2), and three equivalent Al(4) atoms. In the second Al site, Al(2) is bonded to two equivalent Tb(2), two equivalent Al(1), four equivalent Al(3), and four equivalent Al(4) atoms to form AlTb2Al10 cuboctahedra that share corners with four equivalent Al(2)Tb2Al10 cuboctahedra, corners with ten equivalent Al(4)Tb3Al9 cuboctahedra, edges with six equivalent Al(4)Tb3Al9 cuboctahedra, faces with four equivalent Al(4)Tb3Al9 cuboctahedra, and faces with six equivalent Al(2)Tb2Al10 cuboctahedra. In the third Al site, Al(3) is bonded in a 10-coordinate geometry to one Tb(1), one Tb(2), two equivalent Al(2), two equivalent Al(3), and four equivalent Al(4) atoms. In the fourth Al site, Al(4) is bonded to one Tb(2), two equivalent Tb(1), one Al(1), two equivalent Al(2), two equivalent Al(4), and four equivalent Al(3) atoms to form distorted AlTb3Al9 cuboctahedra that share corners with five equivalent Al(2)Tb2Al10 cuboctahedra, corners with ten equivalent Al(4)Tb3Al9 cuboctahedra, edges with three equivalent Al(2)Tb2Al10 cuboctahedra, edges with five equivalent Al(4)Tb3Al9 cuboctahedra, faces with two equivalent Al(2)Tb2Al10 cuboctahedra, and faces with eight equivalent Al(4)Tb3Al9 cuboctahedra.
Tb2Al17 crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 18-coordinate geometry to six equivalent Al(3) and twelve equivalent Al(4) atoms. All Tb(1)-Al(3) bond lengths are 3.29 Å. There are six shorter (3.33 Å) and six longer (3.64 Å) Tb(1)-Al(4) bond lengths. In the second Tb site, Tb(2) is bonded in a 20-coordinate geometry to two equivalent Al(1), six equivalent Al(2), six equivalent Al(3), and six equivalent Al(4) atoms. Both Tb(2)-Al(1) bond lengths are 3.12 Å. All Tb(2)-Al(2) bond lengths are 3.52 Å. All Tb(2)-Al(3) bond lengths are 3.37 Å. All Tb(2)-Al(4) bond lengths are 3.42 Å. There are four inequivalent Al sites. In the first Al site, Al(1) is bonded in a 2-coordinate geometry to one Tb(2), one Al(1), three equivalent Al(2), and three equivalent Al(4) atoms. The Al(1)-Al(1) bond length is 2.64 Å. All Al(1)-Al(2) bond lengths are 2.88 Å. All Al(1)-Al(4) bond lengths are 3.01 Å. In the second Al site, Al(2) is bonded to two equivalent Tb(2), two equivalent Al(1), four equivalent Al(3), and four equivalent Al(4) atoms to form AlTb2Al10 cuboctahedra that share corners with four equivalent Al(2)Tb2Al10 cuboctahedra, corners with ten equivalent Al(4)Tb3Al9 cuboctahedra, edges with six equivalent Al(4)Tb3Al9 cuboctahedra, faces with four equivalent Al(4)Tb3Al9 cuboctahedra, and faces with six equivalent Al(2)Tb2Al10 cuboctahedra. All Al(2)-Al(3) bond lengths are 2.67 Å. All Al(2)-Al(4) bond lengths are 2.77 Å. In the third Al site, Al(3) is bonded in a 10-coordinate geometry to one Tb(1), one Tb(2), two equivalent Al(2), two equivalent Al(3), and four equivalent Al(4) atoms. There is one shorter (2.76 Å) and one longer (2.92 Å) Al(3)-Al(3) bond length. There are two shorter (2.75 Å) and two longer (2.83 Å) Al(3)-Al(4) bond lengths. In the fourth Al site, Al(4) is bonded to one Tb(2), two equivalent Tb(1), one Al(1), two equivalent Al(2), two equivalent Al(4), and four equivalent Al(3) atoms to form distorted AlTb3Al9 cuboctahedra that share corners with five equivalent Al(2)Tb2Al10 cuboctahedra, corners with ten equivalent Al(4)Tb3Al9 cuboctahedra, edges with three equivalent Al(2)Tb2Al10 cuboctahedra, edges with five equivalent Al(4)Tb3Al9 cuboctahedra, faces with two equivalent Al(2)Tb2Al10 cuboctahedra, and faces with eight equivalent Al(4)Tb3Al9 cuboctahedra. Both Al(4)-Al(4) bond lengths are 2.72 Å.