Al8Cr4Er crystallizes in the tetragonal I4/mmm space group. Er(1) is bonded in a 20-coordinate geometry to eight equivalent Cr(1), four equivalent Al(1), and eight equivalent Al(2) atoms. Cr(1) is bonded to two equivalent Er(1), two equivalent Cr(1), four equivalent Al(1), and four equivalent Al(2) atoms to form distorted CrEr2Al8Cr2 cuboctahedra that share corners with eight equivalent Al(2)Er2Al6Cr4 cuboctahedra, corners with ten equivalent Cr(1)Er2Al8Cr2 cuboctahedra, edges with four equivalent Cr(1)Er2Al8Cr2 cuboctahedra, edges with four equivalent Al(2)Er2Al6Cr4 cuboctahedra, faces with six equivalent Cr(1)Er2Al8Cr2 cuboctahedra, and faces with eight equivalent Al(2)Er2Al6Cr4 cuboctahedra. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded in a 10-coordinate geometry to one Er(1), four equivalent Cr(1), one Al(1), and four equivalent Al(2) atoms. In the second Al site, Al(2) is bonded to two equivalent Er(1), four equivalent Cr(1), two equivalent Al(2), and four equivalent Al(1) atoms to form distorted AlEr2Al6Cr4 cuboctahedra that share corners with eight equivalent Cr(1)Er2Al8Cr2 cuboctahedra, corners with ten equivalent Al(2)Er2Al6Cr4 cuboctahedra, edges with three equivalent Al(2)Er2Al6Cr4 cuboctahedra, edges with four equivalent Cr(1)Er2Al8Cr2 cuboctahedra, faces with seven equivalent Al(2)Er2Al6Cr4 cuboctahedra, and faces with eight equivalent Cr(1)Er2Al8Cr2 cuboctahedra.
Al8Cr4Er crystallizes in the tetragonal I4/mmm space group. Er(1) is bonded in a 20-coordinate geometry to eight equivalent Cr(1), four equivalent Al(1), and eight equivalent Al(2) atoms. All Er(1)-Cr(1) bond lengths are 3.39 Å. All Er(1)-Al(1) bond lengths are 2.98 Å. All Er(1)-Al(2) bond lengths are 3.21 Å. Cr(1) is bonded to two equivalent Er(1), two equivalent Cr(1), four equivalent Al(1), and four equivalent Al(2) atoms to form distorted CrEr2Al8Cr2 cuboctahedra that share corners with eight equivalent Al(2)Er2Al6Cr4 cuboctahedra, corners with ten equivalent Cr(1)Er2Al8Cr2 cuboctahedra, edges with four equivalent Cr(1)Er2Al8Cr2 cuboctahedra, edges with four equivalent Al(2)Er2Al6Cr4 cuboctahedra, faces with six equivalent Cr(1)Er2Al8Cr2 cuboctahedra, and faces with eight equivalent Al(2)Er2Al6Cr4 cuboctahedra. Both Cr(1)-Cr(1) bond lengths are 2.53 Å. All Cr(1)-Al(1) bond lengths are 2.67 Å. All Cr(1)-Al(2) bond lengths are 2.57 Å. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded in a 10-coordinate geometry to one Er(1), four equivalent Cr(1), one Al(1), and four equivalent Al(2) atoms. The Al(1)-Al(1) bond length is 2.93 Å. There are two shorter (2.72 Å) and two longer (2.87 Å) Al(1)-Al(2) bond lengths. In the second Al site, Al(2) is bonded to two equivalent Er(1), four equivalent Cr(1), two equivalent Al(2), and four equivalent Al(1) atoms to form distorted AlEr2Al6Cr4 cuboctahedra that share corners with eight equivalent Cr(1)Er2Al8Cr2 cuboctahedra, corners with ten equivalent Al(2)Er2Al6Cr4 cuboctahedra, edges with three equivalent Al(2)Er2Al6Cr4 cuboctahedra, edges with four equivalent Cr(1)Er2Al8Cr2 cuboctahedra, faces with seven equivalent Al(2)Er2Al6Cr4 cuboctahedra, and faces with eight equivalent Cr(1)Er2Al8Cr2 cuboctahedra. Both Al(2)-Al(2) bond lengths are 2.79 Å.