ErTl(WO4)2 crystallizes in the monoclinic C2/c space group. Er(1) is bonded in a 8-coordinate geometry to two equivalent O(3), two equivalent O(4), and four equivalent O(2) atoms. W(1) is bonded to one O(2), one O(4), two equivalent O(1), and two equivalent O(3) atoms to form a mixture of distorted corner and edge-sharing WO6 octahedra. The corner-sharing octahedral tilt angles are 44°. Tl(1) is bonded in a 2-coordinate geometry to two equivalent O(1) atoms. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 1-coordinate geometry to two equivalent W(1) and one Tl(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Er(1) and one W(1) atom. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Er(1) and two equivalent W(1) atoms. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Er(1) and one W(1) atom.
ErTl(WO4)2 crystallizes in the monoclinic C2/c space group. Er(1) is bonded in a 8-coordinate geometry to two equivalent O(3), two equivalent O(4), and four equivalent O(2) atoms. Both Er(1)-O(3) bond lengths are 2.26 Å. Both Er(1)-O(4) bond lengths are 2.24 Å. There are two shorter (2.30 Å) and two longer (2.75 Å) Er(1)-O(2) bond lengths. W(1) is bonded to one O(2), one O(4), two equivalent O(1), and two equivalent O(3) atoms to form a mixture of distorted corner and edge-sharing WO6 octahedra. The corner-sharing octahedral tilt angles are 44°. The W(1)-O(2) bond length is 1.83 Å. The W(1)-O(4) bond length is 1.80 Å. There is one shorter (1.81 Å) and one longer (2.22 Å) W(1)-O(1) bond length. There is one shorter (1.98 Å) and one longer (2.10 Å) W(1)-O(3) bond length. Tl(1) is bonded in a 2-coordinate geometry to two equivalent O(1) atoms. Both Tl(1)-O(1) bond lengths are 2.78 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 1-coordinate geometry to two equivalent W(1) and one Tl(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Er(1) and one W(1) atom. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Er(1) and two equivalent W(1) atoms. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Er(1) and one W(1) atom.