MgH8(C9O4)2 crystallizes in the monoclinic C2/c space group. Mg(1) is bonded in a rectangular see-saw-like geometry to two equivalent O(2) and two equivalent O(4) atoms. Both Mg(1)-O(2) bond lengths are 2.07 Å. Both Mg(1)-O(4) bond lengths are 2.10 Å. There are nine inequivalent C sites. In the first C site, C(1) is bonded in a distorted 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 1.27 Å. The C(1)-O(2) bond length is 1.24 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(6) atom. The C(2)-C(3) bond length is 1.38 Å. The C(2)-C(6) bond length is 1.38 Å. In the third C site, C(3) is bonded in a distorted single-bond geometry to one C(2), one C(4), and one H(2) atom. The C(3)-C(4) bond length is 1.39 Å. The C(3)-H(2) bond length is 0.93 Å. In the fourth C site, C(4) is bonded in a trigonal planar geometry to one C(3), one C(7), and one C(9) atom. The C(4)-C(7) bond length is 1.40 Å. The C(4)-C(9) bond length is 1.43 Å. In the fifth C site, C(5) is bonded in a trigonal planar geometry to one C(6), one C(7), and one C(8) atom. The C(5)-C(6) bond length is 1.38 Å. The C(5)-C(7) bond length is 1.39 Å. The C(5)-C(8) bond length is 1.50 Å. In the sixth C site, C(6) is bonded in a distorted single-bond geometry to one C(2), one C(5), and one H(3) atom. The C(6)-H(3) bond length is 0.93 Å. In the seventh C site, C(7) is bonded in a distorted trigonal planar geometry to one C(4), one C(5), and one H(4) atom. The C(7)-H(4) bond length is 0.93 Å. In the eighth C site, C(8) is bonded in a distorted bent 120 degrees geometry to one C(5), one O(3), and one O(4) atom. The C(8)-O(3) bond length is 1.28 Å. The C(8)-O(4) bond length is 1.23 Å. In the ninth C site, C(9) is bonded in a linear geometry to one C(4) and one C(9) atom. The C(9)-C(9) bond length is 1.20 Å. There are four 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 0.82 Å. The H(1)-O(3) bond length is 1.64 Å. In the second H site, H(2) is bonded in a single-bond geometry to one C(3) atom. In the third H site, H(3) is bonded in a single-bond geometry to one C(6) atom. In the fourth H site, H(4) is bonded in a single-bond geometry to one C(7) atom. There are four inequivalent O sites. In the first O site, O(1) is bonded in a water-like geometry to one C(1) and one H(1) atom. In the second O site, O(2) is bonded in a distorted 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 bent 120 degrees geometry to one C(8) and one H(1) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to one Mg(1) and one C(8) atom. Linkers: 4 [O]C(=O)c1cc(C#Cc2cc(C([O])=O)cc(C(=O)O)c2)cc(C(=O)O)c1. Metal clusters: 4 O[C]O[Mg]O[C]O.[O][C]=O.[O][C]=O. RCSR code: pts. The MOF has largest included sphere 6.47 A, density 1.04 g/cm3, surface area 4619.06 m2/g, accessible volume 0.49 cm3/g