Er2FeC4H2(S2O11)2 crystallizes in the monoclinic C2/c space group. Er(1) is bonded in a 8-coordinate geometry to one O(1), one O(11), one O(2), one O(3), one O(4), one O(5), one O(6), and one O(9) atom. The Er(1)-O(1) bond length is 2.25 Å. The Er(1)-O(11) bond length is 2.40 Å. The Er(1)-O(2) bond length is 2.39 Å. The Er(1)-O(3) bond length is 2.26 Å. The Er(1)-O(4) bond length is 2.31 Å. The Er(1)-O(5) bond length is 2.26 Å. The Er(1)-O(6) bond length is 2.50 Å. The Er(1)-O(9) bond length is 2.39 Å. Fe(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(7) atoms to form FeO6 octahedra that share corners with two equivalent S(1)O4 tetrahedra. Both Fe(1)-O(1) bond lengths are 2.04 Å. Both Fe(1)-O(2) bond lengths are 2.23 Å. Both Fe(1)-O(7) bond lengths are 2.08 Å. There are two inequivalent C sites. In the first C site, C(1) is bonded in a distorted bent 120 degrees geometry to one O(3) and one O(7) atom. The C(1)-O(3) bond length is 1.25 Å. The C(1)-O(7) bond length is 1.25 Å. In the second C site, C(2) is bonded in a distorted water-like geometry to one H(1) and one O(1) atom. The C(2)-H(1) bond length is 0.98 Å. The C(2)-O(1) bond length is 1.43 Å. H(1) is bonded in a single-bond geometry to one C(2) atom. There are two inequivalent S sites. In the first S site, S(1) is bonded to one O(2), one O(4), one O(6), and one O(8) atom to form SO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles are 45°. The S(1)-O(2) bond length is 1.50 Å. The S(1)-O(4) bond length is 1.46 Å. The S(1)-O(6) bond length is 1.49 Å. The S(1)-O(8) bond length is 1.44 Å. In the second S site, S(2) is bonded in a tetrahedral geometry to one O(10), one O(11), one O(5), and one O(9) atom. The S(2)-O(10) bond length is 1.42 Å. The S(2)-O(11) bond length is 1.46 Å. The S(2)-O(5) bond length is 1.45 Å. The S(2)-O(9) bond length is 1.46 Å. There are eleven inequivalent O sites. In the first O site, O(7) is bonded in a bent 120 degrees geometry to one Fe(1) and one C(1) atom. In the second O site, O(1) is bonded in a distorted trigonal planar geometry to one Er(1), one Fe(1), and one C(2) atom. In the third O site, O(2) is bonded in a 3-coordinate geometry to one Er(1), one Fe(1), and one S(1) atom. In the fourth O site, O(3) is bonded in a bent 120 degrees geometry to one Er(1) and one C(1) atom. In the fifth O site, O(4) is bonded in a bent 150 degrees geometry to one Er(1) and one S(1) atom. In the sixth O site, O(5) is bonded in a bent 150 degrees geometry to one Er(1) and one S(2) atom. In the seventh O site, O(8) is bonded in a single-bond geometry to one S(1) atom. In the eighth O site, O(9) is bonded in a distorted water-like geometry to one Er(1) and one S(2) atom. In the ninth O site, O(10) is bonded in a single-bond geometry to one S(2) atom. In the tenth O site, O(11) is bonded in a distorted water-like geometry to one Er(1) and one S(2) atom. In the eleventh O site, O(6) is bonded in a distorted single-bond geometry to one Er(1) and one S(1) atom. Linkers: 3 [O]C(=O)[C@@H]([O])[C@@H]([O])C([O])=O. Metal clusters: 8 [Er] ,4 [Fe]. The MOF has largest included sphere 4.70 A, density 1.92 g/cm3, surface area 2190.72 m2/g, accessible volume 0.29 cm3/g