ErC5H6O8 crystallizes in the orthorhombic Fddd space group. Er(1) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. Both Er(1)-O(1) bond lengths are 2.22 Å. Both Er(1)-O(2) bond lengths are 2.35 Å. Both Er(1)-O(3) bond lengths are 2.41 Å. Both Er(1)-O(4) bond lengths are 2.42 Å. There are three inequivalent C sites. In the first C site, C(3) is bonded in a distorted bent 120 degrees geometry to two equivalent O(3) atoms. Both C(3)-O(3) bond lengths are 1.27 Å. In the second C site, C(1) is bonded in a distorted bent 120 degrees geometry to one C(2), one O(1), and one O(2) atom. The C(1)-C(2) bond length is 1.49 Å. The C(1)-O(1) bond length is 1.28 Å. The C(1)-O(2) bond length is 1.27 Å. In the third C site, C(2) is bonded in a distorted trigonal planar geometry to one C(1), one C(2), and one H(1) atom. The C(2)-C(2) bond length is 1.34 Å. The C(2)-H(1) bond length is 1.09 Å. There are three inequivalent H sites. In the first H site, H(3) is bonded in a distorted single-bond geometry to one O(3) and one O(4) atom. The H(3)-O(3) bond length is 1.70 Å. The H(3)-O(4) bond length is 1.00 Å. In the second H site, H(1) is bonded in a single-bond geometry to one C(2) atom. In the third H site, H(2) is bonded in a single-bond geometry to one O(4) atom. The H(2)-O(4) bond length is 0.97 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to one Er(1) and one C(1) atom. In the second O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Er(1) and one C(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Er(1), one C(3), and one H(3) atom. In the fourth O site, O(4) is bonded in a distorted water-like geometry to one Er(1), one H(2), and one H(3) atom. Linkers: 4 [O]C(=O)/C=C/C([O])=O ,2 [O]C(=O)C([O])=O. Metal clusters: 4 [Er]. The MOF has largest included sphere 2.92 A, density 2.40 g/cm3, surface area 2482.38 m2/g, accessible volume 0.11 cm3/g