MgH4(C2O3)2 crystallizes in the monoclinic C2/c space group. Mg(1) is bonded in an octahedral geometry to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms. Both Mg(1)-O(1) bond lengths are 2.12 Å. Both Mg(1)-O(2) bond lengths are 2.02 Å. Both Mg(1)-O(3) 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(1) and one O(2) atom. The C(1)-O(1) bond length is 1.28 Å. The C(1)-O(2) 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(3) atom. The C(2)-H(1) bond length is 1.10 Å. The C(2)-O(3) bond length is 1.42 Å. There are two inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one C(2) atom. In the second H site, H(2) is bonded in a distorted single-bond geometry to one O(1) and one O(3) atom. The H(2)-O(1) bond length is 1.62 Å. The H(2)-O(3) bond length is 1.01 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Mg(1), one C(1), and one H(2) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Mg(1) and one C(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Mg(1), one C(2), and one H(2) atom. Linkers: 1 [O]C(=O)[C@@H](O)[C@@H](O)C([O])=O. Metal clusters: 2 [Mg]. The MOF has largest included sphere 1.56 A, density 2.01 g/cm3, surface area 3322.05 m2/g, accessible volume 0.05 cm3/g