Er2Cu2O5 is Spinel-like structured and crystallizes in the orthorhombic Pna2_1 space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to one O(1), one O(3), two equivalent O(2), and two equivalent O(5) atoms to form a mixture of distorted corner and edge-sharing ErO6 octahedra. The corner-sharing octahedral tilt angles range from 21-64°. In the second Er site, Er(2) is bonded to one O(3), one O(5), two equivalent O(1), and two equivalent O(4) atoms to form a mixture of corner and edge-sharing ErO6 octahedra. The corner-sharing octahedral tilt angles range from 21-64°. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a rectangular see-saw-like geometry to one O(2), one O(3), one O(4), and one O(5) atom. In the second Cu site, Cu(2) is bonded in a rectangular see-saw-like geometry to one O(1), one O(2), one O(3), and one O(4) atom. There are five inequivalent O sites. In the first O site, O(5) is bonded to one Er(2), two equivalent Er(1), and one Cu(1) atom to form OEr3Cu tetrahedra that share corners with two equivalent O(5)Er3Cu tetrahedra, corners with four equivalent O(1)Er3Cu tetrahedra, corners with three equivalent O(2)Er2Cu2 trigonal pyramids, corners with three equivalent O(4)Er2Cu2 trigonal pyramids, and  an edgeedge with one O(2)Er2Cu2 trigonal pyramid. In the second O site, O(1) is bonded to one Er(1), two equivalent Er(2), and one Cu(2) atom to form OEr3Cu tetrahedra that share corners with two equivalent O(1)Er3Cu tetrahedra, corners with four equivalent O(5)Er3Cu tetrahedra, corners with three equivalent O(2)Er2Cu2 trigonal pyramids, corners with three equivalent O(4)Er2Cu2 trigonal pyramids, and  an edgeedge with one O(4)Er2Cu2 trigonal pyramid. In the third O site, O(2) is bonded to two equivalent Er(1), one Cu(1), and one Cu(2) atom to form OEr2Cu2 trigonal pyramids that share corners with three equivalent O(1)Er3Cu tetrahedra, corners with three equivalent O(5)Er3Cu tetrahedra, corners with two equivalent O(2)Er2Cu2 trigonal pyramids,  an edgeedge with one O(5)Er3Cu tetrahedra, and  an edgeedge with one O(4)Er2Cu2 trigonal pyramid. In the fourth O site, O(3) is bonded in a distorted see-saw-like geometry to one Er(1), one Er(2), one Cu(1), and one Cu(2) atom. In the fifth O site, O(4) is bonded to two equivalent Er(2), one Cu(1), and one Cu(2) atom to form OEr2Cu2 trigonal pyramids that share corners with three equivalent O(1)Er3Cu tetrahedra, corners with three equivalent O(5)Er3Cu tetrahedra, corners with two equivalent O(4)Er2Cu2 trigonal pyramids,  an edgeedge with one O(1)Er3Cu tetrahedra, and  an edgeedge with one O(2)Er2Cu2 trigonal pyramid.
Er2Cu2O5 is Spinel-like structured and crystallizes in the orthorhombic Pna2_1 space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to one O(1), one O(3), two equivalent O(2), and two equivalent O(5) atoms to form a mixture of distorted corner and edge-sharing ErO6 octahedra. The corner-sharing octahedral tilt angles range from 21-64°. The Er(1)-O(1) bond length is 2.22 Å. The Er(1)-O(3) bond length is 2.27 Å. There is one shorter (2.28 Å) and one longer (2.29 Å) Er(1)-O(2) bond length. There is one shorter (2.27 Å) and one longer (2.28 Å) Er(1)-O(5) bond length. In the second Er site, Er(2) is bonded to one O(3), one O(5), two equivalent O(1), and two equivalent O(4) atoms to form a mixture of corner and edge-sharing ErO6 octahedra. The corner-sharing octahedral tilt angles range from 21-64°. The Er(2)-O(3) bond length is 2.27 Å. The Er(2)-O(5) bond length is 2.21 Å. There is one shorter (2.26 Å) and one longer (2.29 Å) Er(2)-O(1) bond length. There is one shorter (2.28 Å) and one longer (2.29 Å) Er(2)-O(4) bond length. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a rectangular see-saw-like geometry to one O(2), one O(3), one O(4), and one O(5) atom. The Cu(1)-O(2) bond length is 1.94 Å. The Cu(1)-O(3) bond length is 1.97 Å. The Cu(1)-O(4) bond length is 2.02 Å. The Cu(1)-O(5) bond length is 2.01 Å. In the second Cu site, Cu(2) is bonded in a rectangular see-saw-like geometry to one O(1), one O(2), one O(3), and one O(4) atom. The Cu(2)-O(1) bond length is 2.00 Å. The Cu(2)-O(2) bond length is 2.01 Å. The Cu(2)-O(3) bond length is 1.97 Å. The Cu(2)-O(4) bond length is 1.95 Å. There are five inequivalent O sites. In the first O site, O(5) is bonded to one Er(2), two equivalent Er(1), and one Cu(1) atom to form OEr3Cu tetrahedra that share corners with two equivalent O(5)Er3Cu tetrahedra, corners with four equivalent O(1)Er3Cu tetrahedra, corners with three equivalent O(2)Er2Cu2 trigonal pyramids, corners with three equivalent O(4)Er2Cu2 trigonal pyramids, and  an edgeedge with one O(2)Er2Cu2 trigonal pyramid. In the second O site, O(1) is bonded to one Er(1), two equivalent Er(2), and one Cu(2) atom to form OEr3Cu tetrahedra that share corners with two equivalent O(1)Er3Cu tetrahedra, corners with four equivalent O(5)Er3Cu tetrahedra, corners with three equivalent O(2)Er2Cu2 trigonal pyramids, corners with three equivalent O(4)Er2Cu2 trigonal pyramids, and  an edgeedge with one O(4)Er2Cu2 trigonal pyramid. In the third O site, O(2) is bonded to two equivalent Er(1), one Cu(1), and one Cu(2) atom to form OEr2Cu2 trigonal pyramids that share corners with three equivalent O(1)Er3Cu tetrahedra, corners with three equivalent O(5)Er3Cu tetrahedra, corners with two equivalent O(2)Er2Cu2 trigonal pyramids,  an edgeedge with one O(5)Er3Cu tetrahedra, and  an edgeedge with one O(4)Er2Cu2 trigonal pyramid. In the fourth O site, O(3) is bonded in a distorted see-saw-like geometry to one Er(1), one Er(2), one Cu(1), and one Cu(2) atom. In the fifth O site, O(4) is bonded to two equivalent Er(2), one Cu(1), and one Cu(2) atom to form OEr2Cu2 trigonal pyramids that share corners with three equivalent O(1)Er3Cu tetrahedra, corners with three equivalent O(5)Er3Cu tetrahedra, corners with two equivalent O(4)Er2Cu2 trigonal pyramids,  an edgeedge with one O(1)Er3Cu tetrahedra, and  an edgeedge with one O(2)Er2Cu2 trigonal pyramid.