ErSO5 crystallizes in the orthorhombic Pccn space group. There are four inequivalent Er sites. In the first Er site, Er(1) is bonded to one O(12), one O(17), one O(2), one O(6), one O(7), and one O(8) atom to form distorted ErO6 pentagonal pyramids that share  a cornercorner with one S(1)O4 tetrahedra,  a cornercorner with one S(2)O4 tetrahedra,  a cornercorner with one S(4)O4 tetrahedra,  an edgeedge with one Er(2)O7 pentagonal bipyramid, and  an edgeedge with one Er(4)O7 pentagonal bipyramid. The Er(1)-O(12) bond length is 2.31 Å. The Er(1)-O(17) bond length is 2.30 Å. The Er(1)-O(2) bond length is 2.37 Å. The Er(1)-O(6) bond length is 2.39 Å. The Er(1)-O(7) bond length is 2.32 Å. The Er(1)-O(8) bond length is 2.31 Å. In the second Er site, Er(2) is bonded to one O(1), one O(19), one O(2), one O(3), one O(4), one O(8), and one O(9) atom to form distorted ErO7 pentagonal bipyramids that share  a cornercorner with one S(2)O4 tetrahedra,  a cornercorner with one S(4)O4 tetrahedra, corners with two equivalent S(1)O4 tetrahedra,  an edgeedge with one Er(4)O7 pentagonal bipyramid, and  an edgeedge with one Er(1)O6 pentagonal pyramid. The Er(2)-O(1) bond length is 2.38 Å. The Er(2)-O(19) bond length is 2.32 Å. The Er(2)-O(2) bond length is 2.38 Å. The Er(2)-O(3) bond length is 2.41 Å. The Er(2)-O(4) bond length is 2.39 Å. The Er(2)-O(8) bond length is 2.30 Å. The Er(2)-O(9) bond length is 2.34 Å. In the third Er site, Er(3) is bonded in a distorted pentagonal planar geometry to one O(16), one O(2), one O(20), one O(4), and one O(6) atom. The Er(3)-O(16) bond length is 2.27 Å. The Er(3)-O(2) bond length is 2.31 Å. The Er(3)-O(20) bond length is 2.32 Å. The Er(3)-O(4) bond length is 2.39 Å. The Er(3)-O(6) bond length is 2.35 Å. In the fourth Er site, Er(4) is bonded to one O(10), one O(13), one O(15), one O(18), one O(4), one O(6), and one O(8) atom to form distorted ErO7 pentagonal bipyramids that share  a cornercorner with one S(2)O4 tetrahedra,  a cornercorner with one S(4)O4 tetrahedra, corners with two equivalent S(3)O4 tetrahedra,  an edgeedge with one Er(2)O7 pentagonal bipyramid, and  an edgeedge with one Er(1)O6 pentagonal pyramid. The Er(4)-O(10) bond length is 2.31 Å. The Er(4)-O(13) bond length is 2.35 Å. The Er(4)-O(15) bond length is 2.32 Å. The Er(4)-O(18) bond length is 2.33 Å. The Er(4)-O(4) bond length is 2.38 Å. The Er(4)-O(6) bond length is 2.31 Å. The Er(4)-O(8) bond length is 2.42 Å. There are four inequivalent S sites. In the first S site, S(1) is bonded to one O(1), one O(3), one O(5), and one O(7) atom to form SO4 tetrahedra that share corners with two equivalent Er(2)O7 pentagonal bipyramids and  a cornercorner with one Er(1)O6 pentagonal pyramid. The S(1)-O(1) bond length is 1.47 Å. The S(1)-O(3) bond length is 1.49 Å. The S(1)-O(5) bond length is 1.46 Å. The S(1)-O(7) bond length is 1.48 Å. In the second S site, S(2) is bonded to one O(10), one O(11), one O(12), and one O(9) atom to form SO4 tetrahedra that share  a cornercorner with one Er(2)O7 pentagonal bipyramid,  a cornercorner with one Er(4)O7 pentagonal bipyramid, and  a cornercorner with one Er(1)O6 pentagonal pyramid. The S(2)-O(10) bond length is 1.48 Å. The S(2)-O(11) bond length is 1.46 Å. The S(2)-O(12) bond length is 1.47 Å. The S(2)-O(9) bond length is 1.48 Å. In the third S site, S(3) is bonded to one O(13), one O(14), one O(15), and one O(16) atom to form SO4 tetrahedra that share corners with two equivalent Er(4)O7 pentagonal bipyramids. The S(3)-O(13) bond length is 1.46 Å. The S(3)-O(14) bond length is 1.46 Å. The S(3)-O(15) bond length is 1.47 Å. The S(3)-O(16) bond length is 1.48 Å. In the fourth S site, S(4) is bonded to one O(17), one O(18), one O(19), and one O(20) atom to form SO4 tetrahedra that share  a cornercorner with one Er(2)O7 pentagonal bipyramid,  a cornercorner with one Er(4)O7 pentagonal bipyramid, and  a cornercorner with one Er(1)O6 pentagonal pyramid. The S(4)-O(17) bond length is 1.47 Å. The S(4)-O(18) bond length is 1.46 Å. The S(4)-O(19) bond length is 1.47 Å. The S(4)-O(20) bond length is 1.47 Å. There are twenty inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Er(2) and one S(1) atom. In the second O site, O(2) is bonded in a trigonal non-coplanar geometry to one Er(1), one Er(2), and one Er(3) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to one Er(2) and one S(1) atom. In the fourth O site, O(4) is bonded in a trigonal non-coplanar geometry to one Er(2), one Er(3), and one Er(4) atom. In the fifth O site, O(5) is bonded in a single-bond geometry to one S(1) atom. In the sixth O site, O(6) is bonded in a trigonal non-coplanar geometry to one Er(1), one Er(3), and one Er(4) atom. In the seventh O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Er(1) and one S(1) atom. In the eighth O site, O(8) is bonded in a trigonal non-coplanar geometry to one Er(1), one Er(2), and one Er(4) atom. In the ninth O site, O(9) is bonded in a distorted bent 120 degrees geometry to one Er(2) and one S(2) atom. In the tenth O site, O(10) is bonded in a distorted bent 120 degrees geometry to one Er(4) and one S(2) atom. In the eleventh O site, O(11) is bonded in a single-bond geometry to one S(2) atom. In the twelfth O site, O(12) is bonded in a bent 150 degrees geometry to one Er(1) and one S(2) atom. In the thirteenth O site, O(13) is bonded in a distorted bent 150 degrees geometry to one Er(4) and one S(3) atom. In the fourteenth O site, O(14) is bonded in a single-bond geometry to one S(3) atom. In the fifteenth O site, O(15) is bonded in a distorted bent 120 degrees geometry to one Er(4) and one S(3) atom. In the sixteenth O site, O(16) is bonded in a distorted bent 150 degrees geometry to one Er(3) and one S(3) atom. In the seventeenth O site, O(17) is bonded in a distorted bent 150 degrees geometry to one Er(1) and one S(4) atom. In the eighteenth O site, O(18) is bonded in a distorted bent 150 degrees geometry to one Er(4) and one S(4) atom. In the nineteenth O site, O(19) is bonded in a distorted bent 120 degrees geometry to one Er(2) and one S(4) atom. In the twentieth O site, O(20) is bonded in a distorted single-bond geometry to one Er(3) and one S(4) atom. Linkers: 32 [O]S([O])(=O)=O. Metal clusters: 32 [Er]. The MOF has largest included sphere 4.70 A, density 3.02 g/cm3, surface area 1589.01 m2/g, accessible volume 0.18 cm3/g