Er2FeSbO7 crystallizes in the orthorhombic Imma space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a distorted body-centered cubic geometry to two equivalent O(1), two equivalent O(3), and four equivalent O(4) atoms. In the second Er site, Er(2) is bonded in a body-centered cubic geometry to two equivalent O(1), two equivalent O(2), and four equivalent O(4) atoms. Fe(1) is bonded to two equivalent O(2) and four equivalent O(4) atoms to form FeO6 octahedra that share corners with two equivalent Fe(1)O6 octahedra and corners with four equivalent Sb(1)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. Sb(1) is bonded to two equivalent O(3) and four equivalent O(4) atoms to form SbO6 octahedra that share corners with two equivalent Sb(1)O6 octahedra and corners with four equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Er(1) and two equivalent Er(2) atoms to form OEr4 tetrahedra that share corners with two equivalent O(2)Er2Fe2 tetrahedra, corners with two equivalent O(3)Er2Sb2 tetrahedra, corners with four equivalent O(1)Er4 tetrahedra, corners with eight equivalent O(4)Er2FeSb tetrahedra,  an edgeedge with one O(2)Er2Fe2 tetrahedra,  an edgeedge with one O(3)Er2Sb2 tetrahedra, and edges with four equivalent O(4)Er2FeSb tetrahedra. In the second O site, O(2) is bonded to two equivalent Er(2) and two equivalent Fe(1) atoms to form distorted OEr2Fe2 tetrahedra that share corners with two equivalent O(1)Er4 tetrahedra, corners with four equivalent O(2)Er2Fe2 tetrahedra, corners with eight equivalent O(4)Er2FeSb tetrahedra,  an edgeedge with one O(1)Er4 tetrahedra, and edges with four equivalent O(4)Er2FeSb tetrahedra. In the third O site, O(3) is bonded to two equivalent Er(1) and two equivalent Sb(1) atoms to form distorted OEr2Sb2 tetrahedra that share corners with two equivalent O(1)Er4 tetrahedra, corners with four equivalent O(3)Er2Sb2 tetrahedra, corners with eight equivalent O(4)Er2FeSb tetrahedra,  an edgeedge with one O(1)Er4 tetrahedra, and edges with four equivalent O(4)Er2FeSb tetrahedra. In the fourth O site, O(4) is bonded to one Er(1), one Er(2), one Fe(1), and one Sb(1) atom to form distorted OEr2FeSb tetrahedra that share corners with two equivalent O(2)Er2Fe2 tetrahedra, corners with two equivalent O(3)Er2Sb2 tetrahedra, corners with two equivalent O(1)Er4 tetrahedra, corners with eight equivalent O(4)Er2FeSb tetrahedra,  an edgeedge with one O(2)Er2Fe2 tetrahedra,  an edgeedge with one O(3)Er2Sb2 tetrahedra,  an edgeedge with one O(1)Er4 tetrahedra, and edges with two equivalent O(4)Er2FeSb tetrahedra.
Er2FeSbO7 crystallizes in the orthorhombic Imma space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a distorted body-centered cubic geometry to two equivalent O(1), two equivalent O(3), and four equivalent O(4) atoms. Both Er(1)-O(1) bond lengths are 2.19 Å. Both Er(1)-O(3) bond lengths are 2.44 Å. All Er(1)-O(4) bond lengths are 2.47 Å. In the second Er site, Er(2) is bonded in a body-centered cubic geometry to two equivalent O(1), two equivalent O(2), and four equivalent O(4) atoms. Both Er(2)-O(1) bond lengths are 2.23 Å. Both Er(2)-O(2) bond lengths are 2.48 Å. All Er(2)-O(4) bond lengths are 2.46 Å. Fe(1) is bonded to two equivalent O(2) and four equivalent O(4) atoms to form FeO6 octahedra that share corners with two equivalent Fe(1)O6 octahedra and corners with four equivalent Sb(1)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. Both Fe(1)-O(2) bond lengths are 1.98 Å. All Fe(1)-O(4) bond lengths are 2.00 Å. Sb(1) is bonded to two equivalent O(3) and four equivalent O(4) atoms to form SbO6 octahedra that share corners with two equivalent Sb(1)O6 octahedra and corners with four equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. Both Sb(1)-O(3) bond lengths are 2.02 Å. All Sb(1)-O(4) bond lengths are 1.99 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Er(1) and two equivalent Er(2) atoms to form OEr4 tetrahedra that share corners with two equivalent O(2)Er2Fe2 tetrahedra, corners with two equivalent O(3)Er2Sb2 tetrahedra, corners with four equivalent O(1)Er4 tetrahedra, corners with eight equivalent O(4)Er2FeSb tetrahedra,  an edgeedge with one O(2)Er2Fe2 tetrahedra,  an edgeedge with one O(3)Er2Sb2 tetrahedra, and edges with four equivalent O(4)Er2FeSb tetrahedra. In the second O site, O(2) is bonded to two equivalent Er(2) and two equivalent Fe(1) atoms to form distorted OEr2Fe2 tetrahedra that share corners with two equivalent O(1)Er4 tetrahedra, corners with four equivalent O(2)Er2Fe2 tetrahedra, corners with eight equivalent O(4)Er2FeSb tetrahedra,  an edgeedge with one O(1)Er4 tetrahedra, and edges with four equivalent O(4)Er2FeSb tetrahedra. In the third O site, O(3) is bonded to two equivalent Er(1) and two equivalent Sb(1) atoms to form distorted OEr2Sb2 tetrahedra that share corners with two equivalent O(1)Er4 tetrahedra, corners with four equivalent O(3)Er2Sb2 tetrahedra, corners with eight equivalent O(4)Er2FeSb tetrahedra,  an edgeedge with one O(1)Er4 tetrahedra, and edges with four equivalent O(4)Er2FeSb tetrahedra. In the fourth O site, O(4) is bonded to one Er(1), one Er(2), one Fe(1), and one Sb(1) atom to form distorted OEr2FeSb tetrahedra that share corners with two equivalent O(2)Er2Fe2 tetrahedra, corners with two equivalent O(3)Er2Sb2 tetrahedra, corners with two equivalent O(1)Er4 tetrahedra, corners with eight equivalent O(4)Er2FeSb tetrahedra,  an edgeedge with one O(2)Er2Fe2 tetrahedra,  an edgeedge with one O(3)Er2Sb2 tetrahedra,  an edgeedge with one O(1)Er4 tetrahedra, and edges with two equivalent O(4)Er2FeSb tetrahedra.