RbErSeO3Cl2 crystallizes in the monoclinic P2_1/c space group. Rb(1) is bonded in a 6-coordinate geometry to one O(2), two equivalent Cl(2), and three equivalent Cl(1) atoms. Er(1) is bonded to one O(2), two equivalent O(1), two equivalent O(3), one Cl(1), and one Cl(2) atom to form edge-sharing ErCl2O5 pentagonal bipyramids. Se(1) is bonded in a trigonal non-coplanar geometry to one O(1), one O(2), and one O(3) atom. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to two equivalent Er(1) and one Se(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Rb(1), one Er(1), and one Se(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to two equivalent Er(1) and one Se(1) atom. There are two inequivalent Cl sites. In the first Cl site, Cl(1) is bonded in a 4-coordinate geometry to three equivalent Rb(1) and one Er(1) atom. In the second Cl site, Cl(2) is bonded in a 3-coordinate geometry to two equivalent Rb(1) and one Er(1) atom.
RbErSeO3Cl2 crystallizes in the monoclinic P2_1/c space group. Rb(1) is bonded in a 6-coordinate geometry to one O(2), two equivalent Cl(2), and three equivalent Cl(1) atoms. The Rb(1)-O(2) bond length is 3.03 Å. There is one shorter (3.33 Å) and one longer (3.50 Å) Rb(1)-Cl(2) bond length. There are a spread of Rb(1)-Cl(1) bond distances ranging from 3.35-3.46 Å. Er(1) is bonded to one O(2), two equivalent O(1), two equivalent O(3), one Cl(1), and one Cl(2) atom to form edge-sharing ErCl2O5 pentagonal bipyramids. The Er(1)-O(2) bond length is 2.29 Å. There is one shorter (2.29 Å) and one longer (2.39 Å) Er(1)-O(1) bond length. There is one shorter (2.29 Å) and one longer (2.41 Å) Er(1)-O(3) bond length. The Er(1)-Cl(1) bond length is 2.65 Å. The Er(1)-Cl(2) bond length is 2.63 Å. Se(1) is bonded in a trigonal non-coplanar geometry to one O(1), one O(2), and one O(3) atom. The Se(1)-O(1) bond length is 1.75 Å. The Se(1)-O(2) bond length is 1.70 Å. The Se(1)-O(3) bond length is 1.75 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to two equivalent Er(1) and one Se(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Rb(1), one Er(1), and one Se(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to two equivalent Er(1) and one Se(1) atom. There are two inequivalent Cl sites. In the first Cl site, Cl(1) is bonded in a 4-coordinate geometry to three equivalent Rb(1) and one Er(1) atom. In the second Cl site, Cl(2) is bonded in a 3-coordinate geometry to two equivalent Rb(1) and one Er(1) atom.