HoAl3 crystallizes in the trigonal R-3m space group. There are two inequivalent Ho sites. In the first Ho site, Ho(1) is bonded to six equivalent Al(1) and six equivalent Al(2) atoms to form HoAl12 cuboctahedra that share corners with six equivalent Ho(1)Al12 cuboctahedra, edges with six equivalent Al(1)Ho4Al8 cuboctahedra, faces with six equivalent Al(1)Ho4Al8 cuboctahedra, and faces with eight equivalent Ho(2)Al12 cuboctahedra. In the second Ho site, Ho(2) is bonded to three equivalent Al(1) and nine equivalent Al(2) atoms to form HoAl12 cuboctahedra that share corners with six equivalent Al(1)Ho4Al8 cuboctahedra, corners with nine equivalent Ho(2)Al12 cuboctahedra, edges with six equivalent Al(1)Ho4Al8 cuboctahedra, faces with three equivalent Ho(2)Al12 cuboctahedra, faces with three equivalent Al(1)Ho4Al8 cuboctahedra, and faces with four equivalent Ho(1)Al12 cuboctahedra. There are two inequivalent Al sites. In the first Al site, Al(2) is bonded in a 10-coordinate geometry to one Ho(1), three equivalent Ho(2), two equivalent Al(1), and four equivalent Al(2) atoms. In the second Al site, Al(1) is bonded to two equivalent Ho(1), two equivalent Ho(2), four equivalent Al(1), and four equivalent Al(2) atoms to form distorted AlHo4Al8 cuboctahedra that share corners with four equivalent Ho(2)Al12 cuboctahedra, corners with six equivalent Al(1)Ho4Al8 cuboctahedra, edges with two equivalent Ho(1)Al12 cuboctahedra, edges with four equivalent Ho(2)Al12 cuboctahedra, edges with four equivalent Al(1)Ho4Al8 cuboctahedra, faces with two equivalent Ho(1)Al12 cuboctahedra, faces with two equivalent Ho(2)Al12 cuboctahedra, and faces with four equivalent Al(1)Ho4Al8 cuboctahedra.
HoAl3 crystallizes in the trigonal R-3m space group. There are two inequivalent Ho sites. In the first Ho site, Ho(1) is bonded to six equivalent Al(1) and six equivalent Al(2) atoms to form HoAl12 cuboctahedra that share corners with six equivalent Ho(1)Al12 cuboctahedra, edges with six equivalent Al(1)Ho4Al8 cuboctahedra, faces with six equivalent Al(1)Ho4Al8 cuboctahedra, and faces with eight equivalent Ho(2)Al12 cuboctahedra. All Ho(1)-Al(1) bond lengths are 3.06 Å. All Ho(1)-Al(2) bond lengths are 3.05 Å. In the second Ho site, Ho(2) is bonded to three equivalent Al(1) and nine equivalent Al(2) atoms to form HoAl12 cuboctahedra that share corners with six equivalent Al(1)Ho4Al8 cuboctahedra, corners with nine equivalent Ho(2)Al12 cuboctahedra, edges with six equivalent Al(1)Ho4Al8 cuboctahedra, faces with three equivalent Ho(2)Al12 cuboctahedra, faces with three equivalent Al(1)Ho4Al8 cuboctahedra, and faces with four equivalent Ho(1)Al12 cuboctahedra. All Ho(2)-Al(1) bond lengths are 3.00 Å. There are three shorter (3.01 Å) and six longer (3.07 Å) Ho(2)-Al(2) bond lengths. There are two inequivalent Al sites. In the first Al site, Al(2) is bonded in a 10-coordinate geometry to one Ho(1), three equivalent Ho(2), two equivalent Al(1), and four equivalent Al(2) atoms. Both Al(2)-Al(1) bond lengths are 2.86 Å. There are two shorter (2.70 Å) and two longer (2.83 Å) Al(2)-Al(2) bond lengths. In the second Al site, Al(1) is bonded to two equivalent Ho(1), two equivalent Ho(2), four equivalent Al(1), and four equivalent Al(2) atoms to form distorted AlHo4Al8 cuboctahedra that share corners with four equivalent Ho(2)Al12 cuboctahedra, corners with six equivalent Al(1)Ho4Al8 cuboctahedra, edges with two equivalent Ho(1)Al12 cuboctahedra, edges with four equivalent Ho(2)Al12 cuboctahedra, edges with four equivalent Al(1)Ho4Al8 cuboctahedra, faces with two equivalent Ho(1)Al12 cuboctahedra, faces with two equivalent Ho(2)Al12 cuboctahedra, and faces with four equivalent Al(1)Ho4Al8 cuboctahedra. All Al(1)-Al(1) bond lengths are 3.06 Å.