ErFeMnO4 crystallizes in the trigonal R3m space group. Er(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted ErO6 octahedra that share corners with three equivalent Mn(1)O5 trigonal bipyramids, corners with three equivalent Fe(1)O5 trigonal bipyramids, and edges with six equivalent Er(1)O6 octahedra. Mn(1) is bonded to one O(2), one O(4), and three equivalent O(3) atoms to form MnO5 trigonal bipyramids that share corners with three equivalent Er(1)O6 octahedra, corners with six equivalent Mn(1)O5 trigonal bipyramids, and edges with three equivalent Fe(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 62°. Fe(1) is bonded to one O(1), one O(3), and three equivalent O(4) atoms to form FeO5 trigonal bipyramids that share corners with three equivalent Er(1)O6 octahedra, corners with six equivalent Fe(1)O5 trigonal bipyramids, and edges with three equivalent Mn(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 66°. There are four inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Er(1) and one Fe(1) atom to form OEr3Fe tetrahedra that share corners with three equivalent O(2)Er3Mn tetrahedra, corners with six equivalent O(1)Er3Fe tetrahedra,  a cornercorner with one O(3)Mn3Fe trigonal pyramid, corners with three equivalent O(4)MnFe3 trigonal pyramids, and edges with three equivalent O(2)Er3Mn tetrahedra. In the second O site, O(2) is bonded to three equivalent Er(1) and one Mn(1) atom to form distorted OEr3Mn tetrahedra that share corners with three equivalent O(1)Er3Fe tetrahedra, corners with six equivalent O(2)Er3Mn tetrahedra,  a cornercorner with one O(4)MnFe3 trigonal pyramid, corners with three equivalent O(3)Mn3Fe trigonal pyramids, and edges with three equivalent O(1)Er3Fe tetrahedra. In the third O site, O(3) is bonded to three equivalent Mn(1) and one Fe(1) atom to form OMn3Fe trigonal pyramids that share  a cornercorner with one O(1)Er3Fe tetrahedra, corners with three equivalent O(2)Er3Mn tetrahedra, corners with six equivalent O(3)Mn3Fe trigonal pyramids, and edges with three equivalent O(4)MnFe3 trigonal pyramids. In the fourth O site, O(4) is bonded to one Mn(1) and three equivalent Fe(1) atoms to form distorted OMnFe3 trigonal pyramids that share  a cornercorner with one O(2)Er3Mn tetrahedra, corners with three equivalent O(1)Er3Fe tetrahedra, corners with six equivalent O(4)MnFe3 trigonal pyramids, and edges with three equivalent O(3)Mn3Fe trigonal pyramids.
ErFeMnO4 crystallizes in the trigonal R3m space group. Er(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted ErO6 octahedra that share corners with three equivalent Mn(1)O5 trigonal bipyramids, corners with three equivalent Fe(1)O5 trigonal bipyramids, and edges with six equivalent Er(1)O6 octahedra. All Er(1)-O(1) bond lengths are 2.25 Å. All Er(1)-O(2) bond lengths are 2.33 Å. Mn(1) is bonded to one O(2), one O(4), and three equivalent O(3) atoms to form MnO5 trigonal bipyramids that share corners with three equivalent Er(1)O6 octahedra, corners with six equivalent Mn(1)O5 trigonal bipyramids, and edges with three equivalent Fe(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 62°. The Mn(1)-O(2) bond length is 1.92 Å. The Mn(1)-O(4) bond length is 1.95 Å. All Mn(1)-O(3) bond lengths are 2.06 Å. Fe(1) is bonded to one O(1), one O(3), and three equivalent O(4) atoms to form FeO5 trigonal bipyramids that share corners with three equivalent Er(1)O6 octahedra, corners with six equivalent Fe(1)O5 trigonal bipyramids, and edges with three equivalent Mn(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 66°. The Fe(1)-O(1) bond length is 1.97 Å. The Fe(1)-O(3) bond length is 2.06 Å. All Fe(1)-O(4) bond lengths are 2.07 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Er(1) and one Fe(1) atom to form OEr3Fe tetrahedra that share corners with three equivalent O(2)Er3Mn tetrahedra, corners with six equivalent O(1)Er3Fe tetrahedra,  a cornercorner with one O(3)Mn3Fe trigonal pyramid, corners with three equivalent O(4)MnFe3 trigonal pyramids, and edges with three equivalent O(2)Er3Mn tetrahedra. In the second O site, O(2) is bonded to three equivalent Er(1) and one Mn(1) atom to form distorted OEr3Mn tetrahedra that share corners with three equivalent O(1)Er3Fe tetrahedra, corners with six equivalent O(2)Er3Mn tetrahedra,  a cornercorner with one O(4)MnFe3 trigonal pyramid, corners with three equivalent O(3)Mn3Fe trigonal pyramids, and edges with three equivalent O(1)Er3Fe tetrahedra. In the third O site, O(3) is bonded to three equivalent Mn(1) and one Fe(1) atom to form OMn3Fe trigonal pyramids that share  a cornercorner with one O(1)Er3Fe tetrahedra, corners with three equivalent O(2)Er3Mn tetrahedra, corners with six equivalent O(3)Mn3Fe trigonal pyramids, and edges with three equivalent O(4)MnFe3 trigonal pyramids. In the fourth O site, O(4) is bonded to one Mn(1) and three equivalent Fe(1) atoms to form distorted OMnFe3 trigonal pyramids that share  a cornercorner with one O(2)Er3Mn tetrahedra, corners with three equivalent O(1)Er3Fe tetrahedra, corners with six equivalent O(4)MnFe3 trigonal pyramids, and edges with three equivalent O(3)Mn3Fe trigonal pyramids.