Er2GeO5 crystallizes in the monoclinic C2/c space group. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded to one O(3), one O(4), one O(5), one O(6), and two equivalent O(1) atoms to form distorted ErO6 octahedra that share  a cornercorner with one Er(2)O6 octahedra,  a cornercorner with one Er(3)O6 octahedra,  a cornercorner with one Ge(1)O4 tetrahedra,  a cornercorner with one Ge(2)O4 tetrahedra,  an edgeedge with one Er(1)O6 octahedra,  an edgeedge with one Er(3)O6 octahedra, edges with two equivalent Er(2)O6 octahedra, and  an edgeedge with one Ge(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 38-39°. In the second Er site, Er(2) is bonded to one O(1), one O(2), one O(3), one O(4), one O(6), and one O(7) atom to form ErO6 octahedra that share  a cornercorner with one Er(1)O6 octahedra,  a cornercorner with one Er(2)O6 octahedra,  a cornercorner with one Ge(2)O4 tetrahedra, corners with three equivalent Ge(1)O4 tetrahedra, edges with two equivalent Er(1)O6 octahedra, and edges with two equivalent Er(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 38-48°. In the third Er site, Er(3) is bonded to one O(1), one O(2), one O(5), one O(7), and two equivalent O(8) atoms to form distorted ErO6 octahedra that share  a cornercorner with one Er(1)O6 octahedra,  a cornercorner with one Er(3)O6 octahedra, corners with two equivalent Ge(1)O4 tetrahedra, corners with two equivalent Ge(2)O4 tetrahedra,  an edgeedge with one Er(1)O6 octahedra,  an edgeedge with one Er(3)O6 octahedra, and edges with two equivalent Er(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 39-57°. There are two inequivalent Ge sites. In the first Ge site, Ge(1) is bonded to one O(2), one O(3), one O(5), and one O(6) atom to form GeO4 tetrahedra that share  a cornercorner with one Er(1)O6 octahedra, corners with two equivalent Er(3)O6 octahedra, corners with three equivalent Er(2)O6 octahedra, and  an edgeedge with one Er(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 22-61°. In the second Ge site, Ge(2) is bonded to two equivalent O(4) and two equivalent O(8) atoms to form GeO4 tetrahedra that share corners with two equivalent Er(1)O6 octahedra, corners with two equivalent Er(2)O6 octahedra, and corners with four equivalent Er(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 44-59°. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Er(2), one Er(3), and two equivalent Er(1) atoms to form edge-sharing OEr4 tetrahedra. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Er(2), one Er(3), and one Ge(1) atom. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Er(1), one Er(2), and one Ge(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Er(1), one Er(2), and one Ge(2) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Er(1), one Er(3), and one Ge(1) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Er(1), one Er(2), and one Ge(1) atom. In the seventh O site, O(7) is bonded to two equivalent Er(2) and two equivalent Er(3) atoms to form distorted edge-sharing OEr4 tetrahedra. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to two equivalent Er(3) and one Ge(2) atom.
Er2GeO5 crystallizes in the monoclinic C2/c space group. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded to one O(3), one O(4), one O(5), one O(6), and two equivalent O(1) atoms to form distorted ErO6 octahedra that share  a cornercorner with one Er(2)O6 octahedra,  a cornercorner with one Er(3)O6 octahedra,  a cornercorner with one Ge(1)O4 tetrahedra,  a cornercorner with one Ge(2)O4 tetrahedra,  an edgeedge with one Er(1)O6 octahedra,  an edgeedge with one Er(3)O6 octahedra, edges with two equivalent Er(2)O6 octahedra, and  an edgeedge with one Ge(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 38-39°. The Er(1)-O(3) bond length is 2.34 Å. The Er(1)-O(4) bond length is 2.23 Å. The Er(1)-O(5) bond length is 2.23 Å. The Er(1)-O(6) bond length is 2.24 Å. There is one shorter (2.18 Å) and one longer (2.23 Å) Er(1)-O(1) bond length. In the second Er site, Er(2) is bonded to one O(1), one O(2), one O(3), one O(4), one O(6), and one O(7) atom to form ErO6 octahedra that share  a cornercorner with one Er(1)O6 octahedra,  a cornercorner with one Er(2)O6 octahedra,  a cornercorner with one Ge(2)O4 tetrahedra, corners with three equivalent Ge(1)O4 tetrahedra, edges with two equivalent Er(1)O6 octahedra, and edges with two equivalent Er(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 38-48°. The Er(2)-O(1) bond length is 2.28 Å. The Er(2)-O(2) bond length is 2.27 Å. The Er(2)-O(3) bond length is 2.18 Å. The Er(2)-O(4) bond length is 2.25 Å. The Er(2)-O(6) bond length is 2.22 Å. The Er(2)-O(7) bond length is 2.23 Å. In the third Er site, Er(3) is bonded to one O(1), one O(2), one O(5), one O(7), and two equivalent O(8) atoms to form distorted ErO6 octahedra that share  a cornercorner with one Er(1)O6 octahedra,  a cornercorner with one Er(3)O6 octahedra, corners with two equivalent Ge(1)O4 tetrahedra, corners with two equivalent Ge(2)O4 tetrahedra,  an edgeedge with one Er(1)O6 octahedra,  an edgeedge with one Er(3)O6 octahedra, and edges with two equivalent Er(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 39-57°. The Er(3)-O(1) bond length is 2.18 Å. The Er(3)-O(2) bond length is 2.24 Å. The Er(3)-O(5) bond length is 2.26 Å. The Er(3)-O(7) bond length is 2.27 Å. There is one shorter (2.20 Å) and one longer (2.33 Å) Er(3)-O(8) bond length. There are two inequivalent Ge sites. In the first Ge site, Ge(1) is bonded to one O(2), one O(3), one O(5), and one O(6) atom to form GeO4 tetrahedra that share  a cornercorner with one Er(1)O6 octahedra, corners with two equivalent Er(3)O6 octahedra, corners with three equivalent Er(2)O6 octahedra, and  an edgeedge with one Er(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 22-61°. The Ge(1)-O(2) bond length is 1.75 Å. The Ge(1)-O(3) bond length is 1.76 Å. The Ge(1)-O(5) bond length is 1.74 Å. The Ge(1)-O(6) bond length is 1.79 Å. In the second Ge site, Ge(2) is bonded to two equivalent O(4) and two equivalent O(8) atoms to form GeO4 tetrahedra that share corners with two equivalent Er(1)O6 octahedra, corners with two equivalent Er(2)O6 octahedra, and corners with four equivalent Er(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 44-59°. Both Ge(2)-O(4) bond lengths are 1.76 Å. Both Ge(2)-O(8) bond lengths are 1.78 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Er(2), one Er(3), and two equivalent Er(1) atoms to form edge-sharing OEr4 tetrahedra. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Er(2), one Er(3), and one Ge(1) atom. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Er(1), one Er(2), and one Ge(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Er(1), one Er(2), and one Ge(2) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Er(1), one Er(3), and one Ge(1) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Er(1), one Er(2), and one Ge(1) atom. In the seventh O site, O(7) is bonded to two equivalent Er(2) and two equivalent Er(3) atoms to form distorted edge-sharing OEr4 tetrahedra. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to two equivalent Er(3) and one Ge(2) atom.