Er4I5 crystallizes in the monoclinic C2/m space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 4-coordinate geometry to one I(1), one I(2), and two equivalent I(3) atoms. In the second Er site, Er(2) is bonded in a 5-coordinate geometry to two equivalent I(1) and three equivalent I(2) atoms. There are three inequivalent I sites. In the first I site, I(1) is bonded in a 3-coordinate geometry to one Er(1) and two equivalent Er(2) atoms. In the second I site, I(2) is bonded in a 4-coordinate geometry to one Er(1) and three equivalent Er(2) atoms. In the third I site, I(3) is bonded in a distorted rectangular see-saw-like geometry to four equivalent Er(1) atoms.
Er4I5 crystallizes in the monoclinic C2/m space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 4-coordinate geometry to one I(1), one I(2), and two equivalent I(3) atoms. The Er(1)-I(1) bond length is 3.08 Å. The Er(1)-I(2) bond length is 3.19 Å. Both Er(1)-I(3) bond lengths are 3.31 Å. In the second Er site, Er(2) is bonded in a 5-coordinate geometry to two equivalent I(1) and three equivalent I(2) atoms. Both Er(2)-I(1) bond lengths are 3.08 Å. There are two shorter (3.12 Å) and one longer (3.45 Å) Er(2)-I(2) bond length. There are three inequivalent I sites. In the first I site, I(1) is bonded in a 3-coordinate geometry to one Er(1) and two equivalent Er(2) atoms. In the second I site, I(2) is bonded in a 4-coordinate geometry to one Er(1) and three equivalent Er(2) atoms. In the third I site, I(3) is bonded in a distorted rectangular see-saw-like geometry to four equivalent Er(1) atoms.