MgC7H3O3 crystallizes in the trigonal R-3 space group. Mg(1) is bonded in a 5-coordinate geometry to one O(1), two equivalent O(2), and two equivalent O(3) atoms. The Mg(1)-O(1) bond length is 1.94 Å. There is one shorter (1.59 Å) and one longer (1.70 Å) Mg(1)-O(2) bond length. There is one shorter (1.65 Å) and one longer (2.01 Å) Mg(1)-O(3) bond length. There are seven inequivalent C sites. In the first C site, C(1) is bonded in a 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 1.29 Å. The C(1)-O(2) bond length is 1.27 Å. In the second C site, C(2) is bonded in a trigonal planar geometry to one C(1), one C(3), and one C(7) atom. The C(2)-C(3) bond length is 1.43 Å. The C(2)-C(7) bond length is 1.58 Å. In the third C site, C(3) is bonded in a distorted single-bond geometry to one C(2) and one O(3) atom. The C(3)-O(3) bond length is 1.41 Å. In the fourth C site, C(4) is bonded in a distorted single-bond geometry to one C(5) and one H(1) atom. The C(4)-C(5) bond length is 1.42 Å. The C(4)-H(1) bond length is 1.08 Å. In the fifth C site, C(5) is bonded in a trigonal planar geometry to one C(4), one C(5), and one C(6) atom. The C(5)-C(5) bond length is 1.55 Å. The C(5)-C(6) bond length is 1.41 Å. In the sixth C site, C(6) is bonded in a distorted trigonal planar geometry to one C(5), one C(7), and one H(3) atom. The C(6)-C(7) bond length is 1.40 Å. The C(6)-H(3) bond length is 1.08 Å. In the seventh C site, C(7) is bonded in a distorted single-bond geometry to one C(2), one C(6), and one H(2) atom. The C(7)-H(2) bond length is 1.09 Å. There are three inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one C(4) atom. In the second H site, H(2) is bonded in a single-bond geometry to one C(7) atom. In the third H site, H(3) is bonded in a single-bond geometry to one C(6) atom. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 120 degrees geometry to one Mg(1) and one C(1) atom. In the second O site, O(2) is bonded in a trigonal planar geometry to two equivalent Mg(1) and one C(1) atom. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Mg(1) and one C(3) atom. Linkers: 3 [O]C(=O)c1ccc(-c2ccc(C([O])=O)c([O])c2)cc1[O] ,2 [O]C(=O)c1ccc(-c2ccc([C]=O)c([O])c2)cc1[O] ,2 [O]C(=O)c1ccc(-c2c[c][c]c([O])c2)cc1[O]. Metal clusters: 6 [Mg]. The MOF has largest included sphere 17.18 A, density 0.61 g/cm3, surface area 3694.91 m2/g, accessible volume 1.16 cm3/g