ErSeO3F crystallizes in the monoclinic P2_1/c space group. Er(1) is bonded in a 8-coordinate geometry to one O(3), two equivalent O(1), three equivalent O(2), and two equivalent F(1) atoms. 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 4-coordinate geometry to three equivalent Er(1) and one Se(1) atom. In the third O site, O(3) is bonded in a bent 120 degrees geometry to one Er(1) and one Se(1) atom. F(1) is bonded in a bent 120 degrees geometry to two equivalent Er(1) atoms.
ErSeO3F crystallizes in the monoclinic P2_1/c space group. Er(1) is bonded in a 8-coordinate geometry to one O(3), two equivalent O(1), three equivalent O(2), and two equivalent F(1) atoms. The Er(1)-O(3) bond length is 2.28 Å. There is one shorter (2.36 Å) and one longer (2.39 Å) Er(1)-O(1) bond length. There are a spread of Er(1)-O(2) bond distances ranging from 2.42-2.64 Å. There is one shorter (2.19 Å) and one longer (2.20 Å) Er(1)-F(1) bond length. 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 1.78 Å. The Se(1)-O(3) bond length is 1.71 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 4-coordinate geometry to three equivalent Er(1) and one Se(1) atom. In the third O site, O(3) is bonded in a bent 120 degrees geometry to one Er(1) and one Se(1) atom. F(1) is bonded in a bent 120 degrees geometry to two equivalent Er(1) atoms.