ErFe6Ge6 crystallizes in the hexagonal P6/mmm space group. Er(1) is bonded to twelve equivalent Fe(1), two equivalent Ge(3), and six equivalent Ge(1) atoms to form distorted face-sharing ErFe12Ge8 hexagonal bipyramids. Fe(1) is bonded in a 12-coordinate geometry to two equivalent Er(1), four equivalent Fe(1), two equivalent Ge(1), two equivalent Ge(2), and two equivalent Ge(3) atoms. There are three inequivalent Ge sites. In the first Ge site, Ge(1) is bonded in a 9-coordinate geometry to three equivalent Er(1) and six equivalent Fe(1) atoms. In the second Ge site, Ge(2) is bonded in a 6-coordinate geometry to six equivalent Fe(1) atoms. In the third Ge site, Ge(3) is bonded in a 8-coordinate geometry to one Er(1), six equivalent Fe(1), and one Ge(3) atom.
ErFe6Ge6 crystallizes in the hexagonal P6/mmm space group. Er(1) is bonded to twelve equivalent Fe(1), two equivalent Ge(3), and six equivalent Ge(1) atoms to form distorted face-sharing ErFe12Ge8 hexagonal bipyramids. All Er(1)-Fe(1) bond lengths are 3.27 Å. Both Er(1)-Ge(3) bond lengths are 2.81 Å. All Er(1)-Ge(1) bond lengths are 2.95 Å. Fe(1) is bonded in a 12-coordinate geometry to two equivalent Er(1), four equivalent Fe(1), two equivalent Ge(1), two equivalent Ge(2), and two equivalent Ge(3) atoms. All Fe(1)-Fe(1) bond lengths are 2.56 Å. Both Fe(1)-Ge(1) bond lengths are 2.51 Å. Both Fe(1)-Ge(2) bond lengths are 2.51 Å. Both Fe(1)-Ge(3) bond lengths are 2.67 Å. There are three inequivalent Ge sites. In the first Ge site, Ge(1) is bonded in a 9-coordinate geometry to three equivalent Er(1) and six equivalent Fe(1) atoms. In the second Ge site, Ge(2) is bonded in a 6-coordinate geometry to six equivalent Fe(1) atoms. In the third Ge site, Ge(3) is bonded in a 8-coordinate geometry to one Er(1), six equivalent Fe(1), and one Ge(3) atom. The Ge(3)-Ge(3) bond length is 2.50 Å.