CaC4H4O6 crystallizes in the orthorhombic C222_1 space group. Ca(1) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(3), and four equivalent O(2) atoms. Both Ca(1)-O(1) bond lengths are 2.46 Å. Both Ca(1)-O(3) bond lengths are 2.37 Å. There are two shorter (2.43 Å) and two longer (2.60 Å) Ca(1)-O(2) bond lengths. 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(1) and one O(2) atom. The C(1)-O(1) bond length is 1.27 Å. The C(1)-O(2) bond length is 1.27 Å. In the second C site, C(2) is bonded in a distorted water-like geometry to one H(2) and one O(3) atom. The C(2)-H(2) bond length is 1.10 Å. The C(2)-O(3) bond length is 1.41 Å. There are two inequivalent H sites. In the first H site, H(1) is bonded in a distorted single-bond geometry to one O(1) and one O(3) atom. The H(1)-O(1) bond length is 1.66 Å. The H(1)-O(3) bond length is 1.00 Å. In the second H site, H(2) is bonded in a single-bond geometry to one C(2) atom. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Ca(1), one C(1), and one H(1) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to two equivalent Ca(1) and one C(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Ca(1), one C(2), and one H(1) atom. Linkers: 2 [O]C(=O)[C@H](O)[C@@H](O)C([O])=O. Metal clusters: 2 [Ca]. The MOF has largest included sphere 1.41 A, density 2.27 g/cm3, surface area 2544.97 m2/g, accessible volume 0.02 cm3/g