ErC4H5O9(CH2)2 crystallizes in the monoclinic P2_1/c space group. The structure consists of eight 02329_fluka molecules inside a ErC4H5O9 framework. In the ErC4H5O9 framework, Er(1) is bonded in a 9-coordinate geometry to one O(1), one O(3), one O(4), one O(5), one O(6), one O(7), one O(8), and two equivalent O(2) atoms. The Er(1)-O(1) bond length is 2.36 Å. The Er(1)-O(3) bond length is 2.41 Å. The Er(1)-O(4) bond length is 2.52 Å. The Er(1)-O(5) bond length is 2.36 Å. The Er(1)-O(6) bond length is 2.32 Å. The Er(1)-O(7) bond length is 2.35 Å. The Er(1)-O(8) bond length is 2.42 Å. There is one shorter (2.38 Å) and one longer (2.40 Å) Er(1)-O(2) bond length. There are four inequivalent C sites. In the first C site, C(1) is bonded in a distorted bent 120 degrees geometry to one O(2) and one O(4) atom. The C(1)-O(2) bond length is 1.30 Å. The C(1)-O(4) bond length is 1.25 Å. In the second C site, C(2) is bonded in a distorted single-bond geometry to one O(7) atom. The C(2)-O(7) bond length is 1.44 Å. In the third C site, C(3) is bonded in a distorted bent 120 degrees geometry to one O(8) and one O(9) atom. The C(3)-O(8) bond length is 1.30 Å. The C(3)-O(9) bond length is 1.26 Å. In the fourth C site, C(5) is bonded in a distorted bent 120 degrees geometry to one O(5) and one O(6) atom. The C(5)-O(5) bond length is 1.28 Å. The C(5)-O(6) bond length is 1.26 Å. There are five inequivalent H sites. In the first H site, H(5) is bonded in a distorted single-bond geometry to one O(7) and one O(9) atom. The H(5)-O(7) bond length is 1.01 Å. The H(5)-O(9) bond length is 1.65 Å. In the second H site, H(6) is bonded in a single-bond geometry to one O(3) and one O(8) atom. The H(6)-O(3) bond length is 1.01 Å. The H(6)-O(8) bond length is 1.70 Å. In the third H site, H(7) is bonded in a single-bond geometry to one O(1) atom. The H(7)-O(1) bond length is 0.97 Å. In the fourth H site, H(8) is bonded in a single-bond geometry to one O(3) atom. The H(8)-O(3) bond length is 0.98 Å. In the fifth H site, H(9) is bonded in a single-bond geometry to one O(1) atom. The H(9)-O(1) bond length is 0.98 Å. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a distorted water-like geometry to one Er(1), one H(7), and one H(9) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to two equivalent Er(1) and one C(1) atom. In the third O site, O(3) is bonded in a water-like geometry to one Er(1), one H(6), and one H(8) atom. In the fourth O site, O(4) is bonded in a single-bond geometry to one Er(1) and one C(1) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Er(1) and one C(5) atom. In the sixth O site, O(6) is bonded in a distorted bent 120 degrees geometry to one Er(1) and one C(5) atom. In the seventh O site, O(7) is bonded in a 2-coordinate geometry to one Er(1), one C(2), and one H(5) atom. In the eighth O site, O(8) is bonded in a distorted single-bond geometry to one Er(1), one C(3), and one H(6) atom. In the ninth O site, O(9) is bonded in a bent 150 degrees geometry to one C(3) and one H(5) atom. Linkers: 4 [O]C(=O)CC(O)(CC([O])=O)C([O])=O. Metal clusters: 4 [Er]. The MOF has largest included sphere 1.82 A, density 2.84 g/cm3, surface area 2029.39 m2/g, accessible volume 0.06 cm3/g