MgC7H4O5CO2 crystallizes in the trigonal P3_121 space group. The structure consists of three carbon dioxide molecules inside a MgC7H4O5 framework. In the MgC7H4O5 framework, Mg(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form corner-sharing MgO6 octahedra. The corner-sharing octahedral tilt angles are 51°. Both Mg(1)-O(1) bond lengths are 2.25 Å. Both Mg(1)-O(2) bond lengths are 2.01 Å. Both Mg(1)-O(3) bond lengths are 2.03 Å. There are five inequivalent C sites. In the first C site, C(5) is bonded in a trigonal planar geometry to one C(3) and two equivalent C(2) atoms. The C(5)-C(3) bond length is 1.48 Å. Both C(5)-C(2) bond lengths are 1.40 Å. In the second C site, C(1) is bonded in a distorted single-bond geometry to one O(3) atom. The C(1)-O(3) bond length is 1.33 Å. In the third C site, C(2) is bonded in a distorted trigonal planar geometry to one C(4), one C(5), and one H(2) atom. The C(2)-C(4) bond length is 1.39 Å. The C(2)-H(2) bond length is 1.09 Å. In the fourth C site, C(3) is bonded in a distorted bent 120 degrees geometry to one C(5) and two equivalent O(2) atoms. Both C(3)-O(2) bond lengths are 1.28 Å. In the fifth C site, C(4) is bonded in a distorted single-bond geometry to one C(2) and one O(1) atom. The C(4)-O(1) bond length is 1.39 Å. There are two inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one O(1) atom. The H(1)-O(1) bond length is 0.98 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 non-coplanar geometry to one Mg(1), one C(4), and one H(1) atom. In the second O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Mg(1) and one C(3) atom. In the third O site, O(3) is bonded in a trigonal planar geometry to two equivalent Mg(1) and one C(1) atom. Linkers: 3 [O]C(=O)c1cc(O)c([O])c(O)c1. Metal clusters: 3 [Mg]. RCSR code: pth. The MOF has largest included sphere 2.22 A, density 1.57 g/cm3, surface area 4161.56 m2/g, accessible volume 0.19 cm3/g