Er(Fe2Al)4 crystallizes in the tetragonal I4/mmm space group. Er(1) is bonded in a 20-coordinate geometry to eight equivalent Fe(1), eight equivalent Fe(2), and four equivalent Al(1) atoms. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent Er(1), two equivalent Fe(1), four equivalent Fe(2), and four equivalent Al(1) atoms to form a mixture of distorted corner, face, and edge-sharing FeEr2Al4Fe6 cuboctahedra. In the second Fe site, Fe(2) is bonded to two equivalent Er(1), two equivalent Fe(2), four equivalent Fe(1), and four equivalent Al(1) atoms to form a mixture of distorted corner, face, and edge-sharing FeEr2Al4Fe6 cuboctahedra. Al(1) is bonded in a 10-coordinate geometry to one Er(1), four equivalent Fe(1), four equivalent Fe(2), and one Al(1) atom.
Er(Fe2Al)4 crystallizes in the tetragonal I4/mmm space group. Er(1) is bonded in a 20-coordinate geometry to eight equivalent Fe(1), eight equivalent Fe(2), and four equivalent Al(1) atoms. All Er(1)-Fe(1) bond lengths are 3.25 Å. All Er(1)-Fe(2) bond lengths are 3.15 Å. All Er(1)-Al(1) bond lengths are 2.92 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent Er(1), two equivalent Fe(1), four equivalent Fe(2), and four equivalent Al(1) atoms to form a mixture of distorted corner, face, and edge-sharing FeEr2Al4Fe6 cuboctahedra. Both Fe(1)-Fe(1) bond lengths are 2.47 Å. All Fe(1)-Fe(2) bond lengths are 2.46 Å. All Fe(1)-Al(1) bond lengths are 2.58 Å. In the second Fe site, Fe(2) is bonded to two equivalent Er(1), two equivalent Fe(2), four equivalent Fe(1), and four equivalent Al(1) atoms to form a mixture of distorted corner, face, and edge-sharing FeEr2Al4Fe6 cuboctahedra. Both Fe(2)-Fe(2) bond lengths are 2.76 Å. There are two shorter (2.65 Å) and two longer (2.66 Å) Fe(2)-Al(1) bond lengths. Al(1) is bonded in a 10-coordinate geometry to one Er(1), four equivalent Fe(1), four equivalent Fe(2), and one Al(1) atom. The Al(1)-Al(1) bond length is 2.64 Å.