Er2(SeO4)3 crystallizes in the monoclinic C2 space group. Er(1) is bonded in a 7-coordinate geometry to one O(1), one O(3), one O(5), two equivalent O(2), and two equivalent O(4) atoms. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 3-coordinate geometry to one O(1), one O(4), and one O(6) atom. In the second Se site, Se(2) is bonded in a tetrahedral geometry to two equivalent O(3) and two equivalent O(5) atoms. There are six inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one Er(1) and one Se(1) atom. In the second O site, O(2) is bonded in a distorted T-shaped geometry to two equivalent Er(1) and one O(4) atom. In the third O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Er(1) and one Se(2) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to two equivalent Er(1), one Se(1), and one O(2) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one Er(1) and one Se(2) atom. In the sixth O site, O(6) is bonded in a single-bond geometry to one Se(1) atom.
Er2(SeO4)3 crystallizes in the monoclinic C2 space group. Er(1) is bonded in a 7-coordinate geometry to one O(1), one O(3), one O(5), two equivalent O(2), and two equivalent O(4) atoms. The Er(1)-O(1) bond length is 2.17 Å. The Er(1)-O(3) bond length is 2.29 Å. The Er(1)-O(5) bond length is 2.44 Å. There is one shorter (2.22 Å) and one longer (2.23 Å) Er(1)-O(2) bond length. There is one shorter (2.32 Å) and one longer (2.56 Å) Er(1)-O(4) bond length. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 3-coordinate geometry to one O(1), one O(4), and one O(6) atom. The Se(1)-O(1) bond length is 1.71 Å. The Se(1)-O(4) bond length is 2.12 Å. The Se(1)-O(6) bond length is 1.63 Å. In the second Se site, Se(2) is bonded in a tetrahedral geometry to two equivalent O(3) and two equivalent O(5) atoms. Both Se(2)-O(3) bond lengths are 1.68 Å. Both Se(2)-O(5) bond lengths are 1.67 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one Er(1) and one Se(1) atom. In the second O site, O(2) is bonded in a distorted T-shaped geometry to two equivalent Er(1) and one O(4) atom. The O(2)-O(4) bond length is 1.50 Å. In the third O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Er(1) and one Se(2) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to two equivalent Er(1), one Se(1), and one O(2) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one Er(1) and one Se(2) atom. In the sixth O site, O(6) is bonded in a single-bond geometry to one Se(1) atom.