Er5(MoO6)2 crystallizes in the monoclinic C2/m space group. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded to one O(4), two equivalent O(1), and four equivalent O(2) atoms to form distorted ErO7 pentagonal bipyramids that share corners with two equivalent Er(3)O6 octahedra,  a cornercorner with one Er(2)O7 pentagonal bipyramid,  an edgeedge with one Er(3)O6 octahedra, edges with two equivalent Mo(1)O6 octahedra, edges with two equivalent Er(1)O7 pentagonal bipyramids, and edges with four equivalent Er(2)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 53°. In the second Er site, Er(2) is bonded to one O(4), two equivalent O(2), and four equivalent O(1) atoms to form distorted ErO7 pentagonal bipyramids that share corners with two equivalent Er(3)O6 octahedra, corners with two equivalent Mo(1)O6 octahedra,  a cornercorner with one Er(1)O7 pentagonal bipyramid, edges with two equivalent Mo(1)O6 octahedra, edges with two equivalent Er(2)O7 pentagonal bipyramids, and edges with four equivalent Er(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 47-56°. In the third Er site, Er(3) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form ErO6 octahedra that share corners with four equivalent Mo(1)O6 octahedra, corners with four equivalent Er(1)O7 pentagonal bipyramids, corners with four equivalent Er(2)O7 pentagonal bipyramids, and edges with two equivalent Er(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 47°. Mo(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form MoO6 octahedra that share corners with two equivalent Er(3)O6 octahedra, corners with two equivalent Er(2)O7 pentagonal bipyramids, edges with two equivalent Mo(1)O6 octahedra, edges with two equivalent Er(1)O7 pentagonal bipyramids, and edges with two equivalent Er(2)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 47°. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Er(1), two equivalent Er(2), and one Mo(1) atom to form distorted OEr3Mo tetrahedra that share corners with four equivalent O(1)Er3Mo tetrahedra, corners with six equivalent O(2)Er4 tetrahedra,  an edgeedge with one O(2)Er4 tetrahedra, and edges with two equivalent O(1)Er3Mo tetrahedra. In the second O site, O(2) is bonded to one Er(2), one Er(3), and two equivalent Er(1) atoms to form OEr4 tetrahedra that share corners with four equivalent O(2)Er4 tetrahedra, corners with six equivalent O(1)Er3Mo tetrahedra,  an edgeedge with one O(1)Er3Mo tetrahedra, and edges with three equivalent O(2)Er4 tetrahedra. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Er(3) and two equivalent Mo(1) atoms. In the fourth O site, O(4) is bonded in a rectangular see-saw-like geometry to one Er(1), one Er(2), and two equivalent Mo(1) atoms.
Er5(MoO6)2 crystallizes in the monoclinic C2/m space group. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded to one O(4), two equivalent O(1), and four equivalent O(2) atoms to form distorted ErO7 pentagonal bipyramids that share corners with two equivalent Er(3)O6 octahedra,  a cornercorner with one Er(2)O7 pentagonal bipyramid,  an edgeedge with one Er(3)O6 octahedra, edges with two equivalent Mo(1)O6 octahedra, edges with two equivalent Er(1)O7 pentagonal bipyramids, and edges with four equivalent Er(2)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 53°. The Er(1)-O(4) bond length is 2.39 Å. Both Er(1)-O(1) bond lengths are 2.39 Å. There are two shorter (2.28 Å) and two longer (2.32 Å) Er(1)-O(2) bond lengths. In the second Er site, Er(2) is bonded to one O(4), two equivalent O(2), and four equivalent O(1) atoms to form distorted ErO7 pentagonal bipyramids that share corners with two equivalent Er(3)O6 octahedra, corners with two equivalent Mo(1)O6 octahedra,  a cornercorner with one Er(1)O7 pentagonal bipyramid, edges with two equivalent Mo(1)O6 octahedra, edges with two equivalent Er(2)O7 pentagonal bipyramids, and edges with four equivalent Er(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 47-56°. The Er(2)-O(4) bond length is 2.29 Å. Both Er(2)-O(2) bond lengths are 2.29 Å. There are two shorter (2.31 Å) and two longer (2.45 Å) Er(2)-O(1) bond lengths. In the third Er site, Er(3) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form ErO6 octahedra that share corners with four equivalent Mo(1)O6 octahedra, corners with four equivalent Er(1)O7 pentagonal bipyramids, corners with four equivalent Er(2)O7 pentagonal bipyramids, and edges with two equivalent Er(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 47°. Both Er(3)-O(3) bond lengths are 2.26 Å. All Er(3)-O(2) bond lengths are 2.34 Å. Mo(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form MoO6 octahedra that share corners with two equivalent Er(3)O6 octahedra, corners with two equivalent Er(2)O7 pentagonal bipyramids, edges with two equivalent Mo(1)O6 octahedra, edges with two equivalent Er(1)O7 pentagonal bipyramids, and edges with two equivalent Er(2)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 47°. Both Mo(1)-O(1) bond lengths are 1.96 Å. Both Mo(1)-O(3) bond lengths are 2.02 Å. Both Mo(1)-O(4) bond lengths are 2.09 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Er(1), two equivalent Er(2), and one Mo(1) atom to form distorted OEr3Mo tetrahedra that share corners with four equivalent O(1)Er3Mo tetrahedra, corners with six equivalent O(2)Er4 tetrahedra,  an edgeedge with one O(2)Er4 tetrahedra, and edges with two equivalent O(1)Er3Mo tetrahedra. In the second O site, O(2) is bonded to one Er(2), one Er(3), and two equivalent Er(1) atoms to form OEr4 tetrahedra that share corners with four equivalent O(2)Er4 tetrahedra, corners with six equivalent O(1)Er3Mo tetrahedra,  an edgeedge with one O(1)Er3Mo tetrahedra, and edges with three equivalent O(2)Er4 tetrahedra. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Er(3) and two equivalent Mo(1) atoms. In the fourth O site, O(4) is bonded in a rectangular see-saw-like geometry to one Er(1), one Er(2), and two equivalent Mo(1) atoms.