TmTb3 is beta Cu3Ti-like structured and crystallizes in the tetragonal I4/mmm space group. Tm(1) is bonded to four equivalent Tb(2) and eight equivalent Tb(1) atoms to form TmTb12 cuboctahedra that share corners with four equivalent Tm(1)Tb12 cuboctahedra, corners with eight equivalent Tb(2)Tb8Tm4 cuboctahedra, edges with eight equivalent Tm(1)Tb12 cuboctahedra, edges with sixteen equivalent Tb(1)Tb8Tm4 cuboctahedra, faces with four equivalent Tm(1)Tb12 cuboctahedra, faces with six equivalent Tb(2)Tb8Tm4 cuboctahedra, and faces with eight equivalent Tb(1)Tb8Tm4 cuboctahedra. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded to four equivalent Tm(1), four equivalent Tb(1), and four equivalent Tb(2) atoms to form TbTb8Tm4 cuboctahedra that share corners with twelve equivalent Tb(1)Tb8Tm4 cuboctahedra, edges with eight equivalent Tm(1)Tb12 cuboctahedra, edges with eight equivalent Tb(1)Tb8Tm4 cuboctahedra, edges with eight equivalent Tb(2)Tb8Tm4 cuboctahedra, faces with four equivalent Tm(1)Tb12 cuboctahedra, faces with four equivalent Tb(2)Tb8Tm4 cuboctahedra, and faces with ten equivalent Tb(1)Tb8Tm4 cuboctahedra. In the second Tb site, Tb(2) is bonded to four equivalent Tm(1) and eight equivalent Tb(1) atoms to form TbTb8Tm4 cuboctahedra that share corners with four equivalent Tb(2)Tb8Tm4 cuboctahedra, corners with eight equivalent Tm(1)Tb12 cuboctahedra, edges with eight equivalent Tb(2)Tb8Tm4 cuboctahedra, edges with sixteen equivalent Tb(1)Tb8Tm4 cuboctahedra, faces with four equivalent Tb(2)Tb8Tm4 cuboctahedra, faces with six equivalent Tm(1)Tb12 cuboctahedra, and faces with eight equivalent Tb(1)Tb8Tm4 cuboctahedra.
TmTb3 is beta Cu3Ti-like structured and crystallizes in the tetragonal I4/mmm space group. Tm(1) is bonded to four equivalent Tb(2) and eight equivalent Tb(1) atoms to form TmTb12 cuboctahedra that share corners with four equivalent Tm(1)Tb12 cuboctahedra, corners with eight equivalent Tb(2)Tb8Tm4 cuboctahedra, edges with eight equivalent Tm(1)Tb12 cuboctahedra, edges with sixteen equivalent Tb(1)Tb8Tm4 cuboctahedra, faces with four equivalent Tm(1)Tb12 cuboctahedra, faces with six equivalent Tb(2)Tb8Tm4 cuboctahedra, and faces with eight equivalent Tb(1)Tb8Tm4 cuboctahedra. All Tm(1)-Tb(2) bond lengths are 3.54 Å. All Tm(1)-Tb(1) bond lengths are 3.55 Å. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded to four equivalent Tm(1), four equivalent Tb(1), and four equivalent Tb(2) atoms to form TbTb8Tm4 cuboctahedra that share corners with twelve equivalent Tb(1)Tb8Tm4 cuboctahedra, edges with eight equivalent Tm(1)Tb12 cuboctahedra, edges with eight equivalent Tb(1)Tb8Tm4 cuboctahedra, edges with eight equivalent Tb(2)Tb8Tm4 cuboctahedra, faces with four equivalent Tm(1)Tb12 cuboctahedra, faces with four equivalent Tb(2)Tb8Tm4 cuboctahedra, and faces with ten equivalent Tb(1)Tb8Tm4 cuboctahedra. All Tb(1)-Tb(1) bond lengths are 3.54 Å. All Tb(1)-Tb(2) bond lengths are 3.55 Å. In the second Tb site, Tb(2) is bonded to four equivalent Tm(1) and eight equivalent Tb(1) atoms to form TbTb8Tm4 cuboctahedra that share corners with four equivalent Tb(2)Tb8Tm4 cuboctahedra, corners with eight equivalent Tm(1)Tb12 cuboctahedra, edges with eight equivalent Tb(2)Tb8Tm4 cuboctahedra, edges with sixteen equivalent Tb(1)Tb8Tm4 cuboctahedra, faces with four equivalent Tb(2)Tb8Tm4 cuboctahedra, faces with six equivalent Tm(1)Tb12 cuboctahedra, and faces with eight equivalent Tb(1)Tb8Tm4 cuboctahedra.