Er6TeO12 crystallizes in the triclinic P-1 space group. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded to one O(5), one O(6), two equivalent O(1), and two equivalent O(2) atoms to form distorted ErO6 pentagonal pyramids that share corners with two equivalent Te(1)O6 octahedra,  an edgeedge with one Te(1)O6 octahedra, and edges with two equivalent Er(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 29-30°. In the second Er site, Er(2) is bonded in a 5-coordinate geometry to one O(3), one O(5), one O(6), and two equivalent O(4) atoms. In the third Er site, Er(3) is bonded in a 5-coordinate geometry to one O(1), one O(3), one O(4), one O(5), and one O(6) atom. Te(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form TeO6 octahedra that share corners with four equivalent Er(1)O6 pentagonal pyramids and edges with two equivalent Er(1)O6 pentagonal pyramids. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Er(3), two equivalent Er(1), and one Te(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Er(1) and one Te(1) atom. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Er(2), one Er(3), and one Te(1) atom. In the fourth O site, O(4) is bonded in a distorted T-shaped geometry to one Er(3) and two equivalent Er(2) atoms. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Er(1), one Er(2), and one Er(3) atom. In the sixth O site, O(6) is bonded in a trigonal non-coplanar geometry to one Er(1), one Er(2), and one Er(3) atom.
Er6TeO12 crystallizes in the triclinic P-1 space group. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded to one O(5), one O(6), two equivalent O(1), and two equivalent O(2) atoms to form distorted ErO6 pentagonal pyramids that share corners with two equivalent Te(1)O6 octahedra,  an edgeedge with one Te(1)O6 octahedra, and edges with two equivalent Er(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 29-30°. The Er(1)-O(5) bond length is 2.20 Å. The Er(1)-O(6) bond length is 2.38 Å. There is one shorter (2.25 Å) and one longer (2.39 Å) Er(1)-O(1) bond length. There is one shorter (2.17 Å) and one longer (2.32 Å) Er(1)-O(2) bond length. In the second Er site, Er(2) is bonded in a 5-coordinate geometry to one O(3), one O(5), one O(6), and two equivalent O(4) atoms. The Er(2)-O(3) bond length is 2.20 Å. The Er(2)-O(5) bond length is 2.34 Å. The Er(2)-O(6) bond length is 2.12 Å. There is one shorter (2.12 Å) and one longer (2.43 Å) Er(2)-O(4) bond length. In the third Er site, Er(3) is bonded in a 5-coordinate geometry to one O(1), one O(3), one O(4), one O(5), and one O(6) atom. The Er(3)-O(1) bond length is 2.56 Å. The Er(3)-O(3) bond length is 2.26 Å. The Er(3)-O(4) bond length is 2.14 Å. The Er(3)-O(5) bond length is 2.15 Å. The Er(3)-O(6) bond length is 2.19 Å. Te(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form TeO6 octahedra that share corners with four equivalent Er(1)O6 pentagonal pyramids and edges with two equivalent Er(1)O6 pentagonal pyramids. Both Te(1)-O(1) bond lengths are 1.93 Å. Both Te(1)-O(2) bond lengths are 1.94 Å. Both Te(1)-O(3) bond lengths are 1.89 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Er(3), two equivalent Er(1), and one Te(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Er(1) and one Te(1) atom. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Er(2), one Er(3), and one Te(1) atom. In the fourth O site, O(4) is bonded in a distorted T-shaped geometry to one Er(3) and two equivalent Er(2) atoms. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Er(1), one Er(2), and one Er(3) atom. In the sixth O site, O(6) is bonded in a trigonal non-coplanar geometry to one Er(1), one Er(2), and one Er(3) atom.