CaH2(C3O2)2 crystallizes in the trigonal R-3 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted face-sharing CaO6 octahedra. All Ca(1)-O(1) bond lengths are 2.25 Å. All Ca(1)-O(2) bond lengths are 2.46 Å. In the second Ca site, Ca(2) is bonded to six equivalent O(2) atoms to form face-sharing CaO6 octahedra. All Ca(2)-O(2) bond lengths are 2.32 Å. There are three inequivalent C sites. In the first C site, C(2) is bonded in a trigonal planar geometry to one C(3) and two equivalent C(1) atoms. The C(2)-C(3) bond length is 1.50 Å. Both C(2)-C(1) bond lengths are 1.40 Å. In the second C site, C(3) is bonded in a distorted bent 120 degrees geometry to one C(2), one O(1), and one O(2) atom. The C(3)-O(1) bond length is 1.26 Å. The C(3)-O(2) bond length is 1.29 Å. In the third C site, C(1) is bonded in a distorted single-bond geometry to two equivalent C(2) and one H(1) atom. The C(1)-H(1) bond length is 1.09 Å. H(1) is bonded in a single-bond geometry to one C(1) atom. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to one Ca(1) and one C(3) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(2), and one C(3) atom. Linkers: 2 [O]C(=O)c1cc(C([O])=O)cc(C([O])=O)c1. Metal clusters: 3 [Ca]. The MOF has largest included sphere 1.45 A, density 1.96 g/cm3, surface area 3460.82 m2/g, accessible volume 0.09 cm3/g