Er6I7 crystallizes in the monoclinic C2/m space group. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded in a 4-coordinate geometry to one I(2), one I(3), and two equivalent I(4) atoms. In the second Er site, Er(2) is bonded in a 3-coordinate geometry to one I(1) and two equivalent I(3) atoms. In the third Er site, Er(3) is bonded in a 4-coordinate geometry to two equivalent I(1) and three equivalent I(2) atoms. There are four inequivalent I sites. In the first I site, I(1) is bonded in a 3-coordinate geometry to one Er(2) and two equivalent Er(3) atoms. In the second I site, I(2) is bonded in a 4-coordinate geometry to one Er(1) and three equivalent Er(3) atoms. In the third I site, I(3) is bonded in a 3-coordinate geometry to one Er(1) and two equivalent Er(2) atoms. In the fourth I site, I(4) is bonded in a distorted rectangular see-saw-like geometry to four equivalent Er(1) atoms.
Er6I7 crystallizes in the monoclinic C2/m space group. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded in a 4-coordinate geometry to one I(2), one I(3), and two equivalent I(4) atoms. The Er(1)-I(2) bond length is 3.18 Å. The Er(1)-I(3) bond length is 2.99 Å. Both Er(1)-I(4) bond lengths are 3.29 Å. In the second Er site, Er(2) is bonded in a 3-coordinate geometry to one I(1) and two equivalent I(3) atoms. The Er(2)-I(1) bond length is 3.27 Å. Both Er(2)-I(3) bond lengths are 3.20 Å. In the third Er site, Er(3) is bonded in a 4-coordinate geometry to two equivalent I(1) and three equivalent I(2) atoms. Both Er(3)-I(1) bond lengths are 3.04 Å. There are two shorter (3.09 Å) and one longer (3.88 Å) Er(3)-I(2) bond length. There are four inequivalent I sites. In the first I site, I(1) is bonded in a 3-coordinate geometry to one Er(2) and two equivalent Er(3) atoms. In the second I site, I(2) is bonded in a 4-coordinate geometry to one Er(1) and three equivalent Er(3) atoms. In the third I site, I(3) is bonded in a 3-coordinate geometry to one Er(1) and two equivalent Er(2) atoms. In the fourth I site, I(4) is bonded in a distorted rectangular see-saw-like geometry to four equivalent Er(1) atoms.