Er2Se3 crystallizes in the orthorhombic Fddd space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form a mixture of corner and edge-sharing ErSe6 octahedra. The corner-sharing octahedral tilt angles range from 3-4°. In the second Er site, Er(2) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form a mixture of corner and edge-sharing ErSe6 octahedra. The corner-sharing octahedral tilt angles are 4°. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a rectangular see-saw-like geometry to two equivalent Er(1) and two equivalent Er(2) atoms. In the second Se site, Se(2) is bonded in a rectangular see-saw-like geometry to two equivalent Er(1) and two equivalent Er(2) atoms.
Er2Se3 crystallizes in the orthorhombic Fddd space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form a mixture of corner and edge-sharing ErSe6 octahedra. The corner-sharing octahedral tilt angles range from 3-4°. Both Er(1)-Se(2) bond lengths are 2.85 Å. All Er(1)-Se(1) bond lengths are 2.82 Å. In the second Er site, Er(2) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form a mixture of corner and edge-sharing ErSe6 octahedra. The corner-sharing octahedral tilt angles are 4°. Both Er(2)-Se(2) bond lengths are 2.83 Å. There are two shorter (2.82 Å) and two longer (2.85 Å) Er(2)-Se(1) bond lengths. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a rectangular see-saw-like geometry to two equivalent Er(1) and two equivalent Er(2) atoms. In the second Se site, Se(2) is bonded in a rectangular see-saw-like geometry to two equivalent Er(1) and two equivalent Er(2) atoms.