Er2Sn2O7 crystallizes in the cubic Fd-3m space group. Er(1) is bonded in a body-centered cubic geometry to two equivalent O(1) and six equivalent O(2) atoms. Sn(1) is bonded to six equivalent O(2) atoms to form corner-sharing SnO6 octahedra. The corner-sharing octahedral tilt angles are 54°. There are two inequivalent O sites. In the first O site, O(1) is bonded to four equivalent Er(1) atoms to form OEr4 tetrahedra that share corners with four equivalent O(1)Er4 tetrahedra, corners with twelve equivalent O(2)Er2Sn2 tetrahedra, and edges with six equivalent O(2)Er2Sn2 tetrahedra. In the second O site, O(2) is bonded to two equivalent Er(1) and two equivalent Sn(1) atoms to form distorted OEr2Sn2 tetrahedra that share corners with two equivalent O(1)Er4 tetrahedra, corners with twelve equivalent O(2)Er2Sn2 tetrahedra,  an edgeedge with one O(1)Er4 tetrahedra, and edges with four equivalent O(2)Er2Sn2 tetrahedra.
Er2Sn2O7 crystallizes in the cubic Fd-3m space group. Er(1) is bonded in a body-centered cubic geometry to two equivalent O(1) and six equivalent O(2) atoms. Both Er(1)-O(1) bond lengths are 2.24 Å. All Er(1)-O(2) bond lengths are 2.47 Å. Sn(1) is bonded to six equivalent O(2) atoms to form corner-sharing SnO6 octahedra. The corner-sharing octahedral tilt angles are 54°. All Sn(1)-O(2) bond lengths are 2.05 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded to four equivalent Er(1) atoms to form OEr4 tetrahedra that share corners with four equivalent O(1)Er4 tetrahedra, corners with twelve equivalent O(2)Er2Sn2 tetrahedra, and edges with six equivalent O(2)Er2Sn2 tetrahedra. In the second O site, O(2) is bonded to two equivalent Er(1) and two equivalent Sn(1) atoms to form distorted OEr2Sn2 tetrahedra that share corners with two equivalent O(1)Er4 tetrahedra, corners with twelve equivalent O(2)Er2Sn2 tetrahedra,  an edgeedge with one O(1)Er4 tetrahedra, and edges with four equivalent O(2)Er2Sn2 tetrahedra.