Ta3Co8Al is Hexagonal Laves-derived structured and crystallizes in the trigonal R3m space group. There are three inequivalent Ta sites. In the first Ta site, Ta(1) is bonded in a 16-coordinate geometry to one Ta(3), three equivalent Ta(2), three equivalent Co(1), three equivalent Co(4), and six equivalent Co(2) atoms. In the second Ta site, Ta(2) is bonded in a 16-coordinate geometry to three equivalent Ta(1), three equivalent Co(2), three equivalent Co(4), six equivalent Co(1), and one Al(1) atom. In the third Ta site, Ta(3) is bonded in a 16-coordinate geometry to one Ta(1), three equivalent Co(1), three equivalent Co(3), six equivalent Co(2), and three equivalent Al(1) atoms. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded to one Ta(1), one Ta(3), two equivalent Ta(2), one Co(3), one Co(4), four equivalent Co(1), and two equivalent Al(1) atoms to form CoTa4Al2Co6 cuboctahedra that share corners with two equivalent Co(3)Ta3Al3Co6 cuboctahedra, corners with two equivalent Co(4)Ta6Co6 cuboctahedra, corners with four equivalent Co(1)Ta4Al2Co6 cuboctahedra, corners with ten equivalent Co(2)Ta5AlCo6 cuboctahedra, edges with two equivalent Co(1)Ta4Al2Co6 cuboctahedra, edges with four equivalent Co(2)Ta5AlCo6 cuboctahedra, faces with three equivalent Co(3)Ta3Al3Co6 cuboctahedra, faces with three equivalent Co(4)Ta6Co6 cuboctahedra, faces with four equivalent Co(2)Ta5AlCo6 cuboctahedra, and faces with eight equivalent Co(1)Ta4Al2Co6 cuboctahedra. In the second Co site, Co(2) is bonded to one Ta(2), two equivalent Ta(1), two equivalent Ta(3), one Co(3), one Co(4), four equivalent Co(2), and one Al(1) atom to form CoTa5AlCo6 cuboctahedra that share corners with two equivalent Co(3)Ta3Al3Co6 cuboctahedra, corners with two equivalent Co(4)Ta6Co6 cuboctahedra, corners with four equivalent Co(2)Ta5AlCo6 cuboctahedra, corners with ten equivalent Co(1)Ta4Al2Co6 cuboctahedra, edges with two equivalent Co(2)Ta5AlCo6 cuboctahedra, edges with four equivalent Co(1)Ta4Al2Co6 cuboctahedra, faces with three equivalent Co(3)Ta3Al3Co6 cuboctahedra, faces with three equivalent Co(4)Ta6Co6 cuboctahedra, faces with four equivalent Co(1)Ta4Al2Co6 cuboctahedra, and faces with eight equivalent Co(2)Ta5AlCo6 cuboctahedra. In the third Co site, Co(3) is bonded to three equivalent Ta(3), three equivalent Co(1), three equivalent Co(2), and three equivalent Al(1) atoms to form CoTa3Al3Co6 cuboctahedra that share corners with six equivalent Co(1)Ta4Al2Co6 cuboctahedra, corners with six equivalent Co(2)Ta5AlCo6 cuboctahedra, corners with six equivalent Co(4)Ta6Co6 cuboctahedra, edges with six equivalent Co(3)Ta3Al3Co6 cuboctahedra, faces with nine equivalent Co(1)Ta4Al2Co6 cuboctahedra, and faces with nine equivalent Co(2)Ta5AlCo6 cuboctahedra. In the fourth Co site, Co(4) is bonded to three equivalent Ta(1), three equivalent Ta(2), three equivalent Co(1), and three equivalent Co(2) atoms to form CoTa6Co6 cuboctahedra that share corners with six equivalent Co(3)Ta3Al3Co6 cuboctahedra, corners with six equivalent Co(1)Ta4Al2Co6 cuboctahedra, corners with six equivalent Co(2)Ta5AlCo6 cuboctahedra, edges with six equivalent Co(4)Ta6Co6 cuboctahedra, faces with nine equivalent Co(1)Ta4Al2Co6 cuboctahedra, and faces with nine equivalent Co(2)Ta5AlCo6 cuboctahedra. Al(1) is bonded in a 16-coordinate geometry to one Ta(2), three equivalent Ta(3), three equivalent Co(2), three equivalent Co(3), and six equivalent Co(1) atoms.
Ta3Co8Al is Hexagonal Laves-derived structured and crystallizes in the trigonal R3m space group. There are three inequivalent Ta sites. In the first Ta site, Ta(1) is bonded in a 16-coordinate geometry to one Ta(3), three equivalent Ta(2), three equivalent Co(1), three equivalent Co(4), and six equivalent Co(2) atoms. The Ta(1)-Ta(3) bond length is 2.90 Å. All Ta(1)-Ta(2) bond lengths are 2.95 Å. All Ta(1)-Co(1) bond lengths are 2.81 Å. All Ta(1)-Co(4) bond lengths are 2.79 Å. All Ta(1)-Co(2) bond lengths are 2.76 Å. In the second Ta site, Ta(2) is bonded in a 16-coordinate geometry to three equivalent Ta(1), three equivalent Co(2), three equivalent Co(4), six equivalent Co(1), and one Al(1) atom. All Ta(2)-Co(2) bond lengths are 2.83 Å. All Ta(2)-Co(4) bond lengths are 2.80 Å. All Ta(2)-Co(1) bond lengths are 2.75 Å. The Ta(2)-Al(1) bond length is 2.85 Å. In the third Ta site, Ta(3) is bonded in a 16-coordinate geometry to one Ta(1), three equivalent Co(1), three equivalent Co(3), six equivalent Co(2), and three equivalent Al(1) atoms. All Ta(3)-Co(1) bond lengths are 2.75 Å. All Ta(3)-Co(3) bond lengths are 2.78 Å. All Ta(3)-Co(2) bond lengths are 2.81 Å. All Ta(3)-Al(1) bond lengths are 2.89 Å. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded to one Ta(1), one Ta(3), two equivalent Ta(2), one Co(3), one Co(4), four equivalent Co(1), and two equivalent Al(1) atoms to form CoTa4Al2Co6 cuboctahedra that share corners with two equivalent Co(3)Ta3Al3Co6 cuboctahedra, corners with two equivalent Co(4)Ta6Co6 cuboctahedra, corners with four equivalent Co(1)Ta4Al2Co6 cuboctahedra, corners with ten equivalent Co(2)Ta5AlCo6 cuboctahedra, edges with two equivalent Co(1)Ta4Al2Co6 cuboctahedra, edges with four equivalent Co(2)Ta5AlCo6 cuboctahedra, faces with three equivalent Co(3)Ta3Al3Co6 cuboctahedra, faces with three equivalent Co(4)Ta6Co6 cuboctahedra, faces with four equivalent Co(2)Ta5AlCo6 cuboctahedra, and faces with eight equivalent Co(1)Ta4Al2Co6 cuboctahedra. The Co(1)-Co(3) bond length is 2.35 Å. The Co(1)-Co(4) bond length is 2.37 Å. There are two shorter (2.36 Å) and two longer (2.39 Å) Co(1)-Co(1) bond lengths. Both Co(1)-Al(1) bond lengths are 2.79 Å. In the second Co site, Co(2) is bonded to one Ta(2), two equivalent Ta(1), two equivalent Ta(3), one Co(3), one Co(4), four equivalent Co(2), and one Al(1) atom to form CoTa5AlCo6 cuboctahedra that share corners with two equivalent Co(3)Ta3Al3Co6 cuboctahedra, corners with two equivalent Co(4)Ta6Co6 cuboctahedra, corners with four equivalent Co(2)Ta5AlCo6 cuboctahedra, corners with ten equivalent Co(1)Ta4Al2Co6 cuboctahedra, edges with two equivalent Co(2)Ta5AlCo6 cuboctahedra, edges with four equivalent Co(1)Ta4Al2Co6 cuboctahedra, faces with three equivalent Co(3)Ta3Al3Co6 cuboctahedra, faces with three equivalent Co(4)Ta6Co6 cuboctahedra, faces with four equivalent Co(1)Ta4Al2Co6 cuboctahedra, and faces with eight equivalent Co(2)Ta5AlCo6 cuboctahedra. The Co(2)-Co(3) bond length is 2.40 Å. The Co(2)-Co(4) bond length is 2.35 Å. There are two shorter (2.36 Å) and two longer (2.39 Å) Co(2)-Co(2) bond lengths. The Co(2)-Al(1) bond length is 2.77 Å. In the third Co site, Co(3) is bonded to three equivalent Ta(3), three equivalent Co(1), three equivalent Co(2), and three equivalent Al(1) atoms to form CoTa3Al3Co6 cuboctahedra that share corners with six equivalent Co(1)Ta4Al2Co6 cuboctahedra, corners with six equivalent Co(2)Ta5AlCo6 cuboctahedra, corners with six equivalent Co(4)Ta6Co6 cuboctahedra, edges with six equivalent Co(3)Ta3Al3Co6 cuboctahedra, faces with nine equivalent Co(1)Ta4Al2Co6 cuboctahedra, and faces with nine equivalent Co(2)Ta5AlCo6 cuboctahedra. All Co(3)-Al(1) bond lengths are 2.78 Å. In the fourth Co site, Co(4) is bonded to three equivalent Ta(1), three equivalent Ta(2), three equivalent Co(1), and three equivalent Co(2) atoms to form CoTa6Co6 cuboctahedra that share corners with six equivalent Co(3)Ta3Al3Co6 cuboctahedra, corners with six equivalent Co(1)Ta4Al2Co6 cuboctahedra, corners with six equivalent Co(2)Ta5AlCo6 cuboctahedra, edges with six equivalent Co(4)Ta6Co6 cuboctahedra, faces with nine equivalent Co(1)Ta4Al2Co6 cuboctahedra, and faces with nine equivalent Co(2)Ta5AlCo6 cuboctahedra. Al(1) is bonded in a 16-coordinate geometry to one Ta(2), three equivalent Ta(3), three equivalent Co(2), three equivalent Co(3), and six equivalent Co(1) atoms.