Tb2CoAl3 crystallizes in the trigonal R-3m space group. Tb(1) is bonded in a 12-coordinate geometry to three equivalent Co(1) and nine equivalent Al(1) atoms. Co(1) is bonded to six equivalent Tb(1) and six equivalent Al(1) atoms to form CoTb6Al6 cuboctahedra that share corners with six equivalent Co(1)Tb6Al6 cuboctahedra, corners with twelve equivalent Al(1)Tb6Al4Co2 cuboctahedra, edges with six equivalent Co(1)Tb6Al6 cuboctahedra, and faces with eighteen equivalent Al(1)Tb6Al4Co2 cuboctahedra. Al(1) is bonded to six equivalent Tb(1), two equivalent Co(1), and four equivalent Al(1) atoms to form distorted AlTb6Al4Co2 cuboctahedra that share corners with four equivalent Co(1)Tb6Al6 cuboctahedra, corners with fourteen equivalent Al(1)Tb6Al4Co2 cuboctahedra, edges with six equivalent Al(1)Tb6Al4Co2 cuboctahedra, faces with six equivalent Co(1)Tb6Al6 cuboctahedra, and faces with twelve equivalent Al(1)Tb6Al4Co2 cuboctahedra.
Tb2CoAl3 crystallizes in the trigonal R-3m space group. Tb(1) is bonded in a 12-coordinate geometry to three equivalent Co(1) and nine equivalent Al(1) atoms. All Tb(1)-Co(1) bond lengths are 3.22 Å. There are three shorter (3.12 Å) and six longer (3.20 Å) Tb(1)-Al(1) bond lengths. Co(1) is bonded to six equivalent Tb(1) and six equivalent Al(1) atoms to form CoTb6Al6 cuboctahedra that share corners with six equivalent Co(1)Tb6Al6 cuboctahedra, corners with twelve equivalent Al(1)Tb6Al4Co2 cuboctahedra, edges with six equivalent Co(1)Tb6Al6 cuboctahedra, and faces with eighteen equivalent Al(1)Tb6Al4Co2 cuboctahedra. All Co(1)-Al(1) bond lengths are 2.69 Å. Al(1) is bonded to six equivalent Tb(1), two equivalent Co(1), and four equivalent Al(1) atoms to form distorted AlTb6Al4Co2 cuboctahedra that share corners with four equivalent Co(1)Tb6Al6 cuboctahedra, corners with fourteen equivalent Al(1)Tb6Al4Co2 cuboctahedra, edges with six equivalent Al(1)Tb6Al4Co2 cuboctahedra, faces with six equivalent Co(1)Tb6Al6 cuboctahedra, and faces with twelve equivalent Al(1)Tb6Al4Co2 cuboctahedra. All Al(1)-Al(1) bond lengths are 2.75 Å.