Co4Al crystallizes in the trigonal R-3m space group. There are three inequivalent Co sites. In the first Co site, Co(1) is bonded to three equivalent Co(2), six equivalent Co(1), and three equivalent Al(1) atoms to form distorted CoAl3Co9 cuboctahedra that share corners with three equivalent Co(2)Co12 cuboctahedra; corners with nine equivalent Co(1)Al3Co9 cuboctahedra; edges with six equivalent Al(1)Al6Co6 cuboctahedra; edges with nine equivalent Co(1)Al3Co9 cuboctahedra; edges with nine Co(2,2)Co12 cuboctahedra; faces with six equivalent Co(1)Al3Co9 cuboctahedra; faces with six equivalent Co(2)Co12 cuboctahedra; and faces with six equivalent Al(1)Al6Co6 cuboctahedra. In the second Co site, Co(2) is bonded to three equivalent Co(1) and nine Co(2,2) atoms to form CoCo12 cuboctahedra that share corners with three equivalent Co(1)Al3Co9 cuboctahedra; corners with three equivalent Al(1)Al6Co6 cuboctahedra; corners with six equivalent Co(2)Co12 cuboctahedra; edges with three equivalent Al(1)Al6Co6 cuboctahedra; edges with nine equivalent Co(1)Al3Co9 cuboctahedra; edges with twelve Co(2,2)Co12 cuboctahedra; faces with six equivalent Co(1)Al3Co9 cuboctahedra; and faces with twelve Co(2,2)Co12 cuboctahedra. In the third Co site, Co(2) is bonded to three equivalent Co(1) and nine Co(2,2) atoms to form CoCo12 cuboctahedra that share corners with three equivalent Co(1)Al3Co9 cuboctahedra; corners with three equivalent Al(1)Al6Co6 cuboctahedra; corners with six equivalent Co(2)Co12 cuboctahedra; edges with three equivalent Al(1)Al6Co6 cuboctahedra; edges with nine equivalent Co(1)Al3Co9 cuboctahedra; edges with twelve Co(2,2)Co12 cuboctahedra; faces with six equivalent Co(1)Al3Co9 cuboctahedra; and faces with twelve Co(2,2)Co12 cuboctahedra. Al(1) is bonded to six equivalent Co(1) and six equivalent Al(1) atoms to form distorted AlAl6Co6 cuboctahedra that share corners with six equivalent Co(2)Co12 cuboctahedra, corners with six equivalent Al(1)Al6Co6 cuboctahedra, edges with six equivalent Co(2)Co12 cuboctahedra, edges with six equivalent Al(1)Al6Co6 cuboctahedra, edges with twelve equivalent Co(1)Al3Co9 cuboctahedra, faces with six equivalent Al(1)Al6Co6 cuboctahedra, and faces with twelve equivalent Co(1)Al3Co9 cuboctahedra.
Co4Al crystallizes in the trigonal R-3m space group. There are three inequivalent Co sites. In the first Co site, Co(1) is bonded to three equivalent Co(2), six equivalent Co(1), and three equivalent Al(1) atoms to form distorted CoAl3Co9 cuboctahedra that share corners with three equivalent Co(2)Co12 cuboctahedra; corners with nine equivalent Co(1)Al3Co9 cuboctahedra; edges with six equivalent Al(1)Al6Co6 cuboctahedra; edges with nine equivalent Co(1)Al3Co9 cuboctahedra; edges with nine Co(2,2)Co12 cuboctahedra; faces with six equivalent Co(1)Al3Co9 cuboctahedra; faces with six equivalent Co(2)Co12 cuboctahedra; and faces with six equivalent Al(1)Al6Co6 cuboctahedra. All Co(1)-Co(2) bond lengths are 2.45 Å. All Co(1)-Co(1) bond lengths are 2.58 Å. All Co(1)-Al(1) bond lengths are 2.52 Å. In the second Co site, Co(2) is bonded to three equivalent Co(1) and nine Co(2,2) atoms to form CoCo12 cuboctahedra that share corners with three equivalent Co(1)Al3Co9 cuboctahedra; corners with three equivalent Al(1)Al6Co6 cuboctahedra; corners with six equivalent Co(2)Co12 cuboctahedra; edges with three equivalent Al(1)Al6Co6 cuboctahedra; edges with nine equivalent Co(1)Al3Co9 cuboctahedra; edges with twelve Co(2,2)Co12 cuboctahedra; faces with six equivalent Co(1)Al3Co9 cuboctahedra; and faces with twelve Co(2,2)Co12 cuboctahedra. There are three shorter (2.50 Å) and six longer (2.58 Å) Co(2)-Co(2,2) bond lengths. In the third Co site, Co(2) is bonded to three equivalent Co(1) and nine Co(2,2) atoms to form CoCo12 cuboctahedra that share corners with three equivalent Co(1)Al3Co9 cuboctahedra; corners with three equivalent Al(1)Al6Co6 cuboctahedra; corners with six equivalent Co(2)Co12 cuboctahedra; edges with three equivalent Al(1)Al6Co6 cuboctahedra; edges with nine equivalent Co(1)Al3Co9 cuboctahedra; edges with twelve Co(2,2)Co12 cuboctahedra; faces with six equivalent Co(1)Al3Co9 cuboctahedra; and faces with twelve Co(2,2)Co12 cuboctahedra. All Co(2)-Co(1) bond lengths are 2.45 Å. All Co(2)-Co(2) bond lengths are 2.58 Å. Al(1) is bonded to six equivalent Co(1) and six equivalent Al(1) atoms to form distorted AlAl6Co6 cuboctahedra that share corners with six equivalent Co(2)Co12 cuboctahedra, corners with six equivalent Al(1)Al6Co6 cuboctahedra, edges with six equivalent Co(2)Co12 cuboctahedra, edges with six equivalent Al(1)Al6Co6 cuboctahedra, edges with twelve equivalent Co(1)Al3Co9 cuboctahedra, faces with six equivalent Al(1)Al6Co6 cuboctahedra, and faces with twelve equivalent Co(1)Al3Co9 cuboctahedra. All Al(1)-Al(1) bond lengths are 2.58 Å.