Mg5H6(C10O9)2 crystallizes in the triclinic P-1 space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(1), one O(6), one O(7), one O(8), and one O(9) atom to form distorted MgO5 square pyramids that share  a cornercorner with one Mg(3)O6 octahedra and corners with two equivalent Mg(2)O5 square pyramids. The corner-sharing octahedral tilt angles are 62°. The Mg(1)-O(1) bond length is 2.04 Å. The Mg(1)-O(6) bond length is 2.05 Å. The Mg(1)-O(7) bond length is 2.17 Å. The Mg(1)-O(8) bond length is 2.26 Å. The Mg(1)-O(9) bond length is 2.02 Å. In the second Mg site, Mg(2) is bonded to one O(2), one O(4), one O(5), one O(8), and one O(9) atom to form MgO5 square pyramids that share corners with two equivalent Mg(1)O5 square pyramids and  an edgeedge with one Mg(3)O6 octahedra. The Mg(2)-O(2) bond length is 2.06 Å. The Mg(2)-O(4) bond length is 2.04 Å. The Mg(2)-O(5) bond length is 2.13 Å. The Mg(2)-O(8) bond length is 2.06 Å. The Mg(2)-O(9) bond length is 2.09 Å. In the third Mg site, Mg(3) is bonded to two equivalent O(3), two equivalent O(5), and two equivalent O(9) atoms to form a mixture of edge and corner-sharing MgO6 octahedra. Both Mg(3)-O(3) bond lengths are 2.05 Å. Both Mg(3)-O(5) bond lengths are 2.13 Å. Both Mg(3)-O(9) bond lengths are 2.08 Å. There are ten 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 1.51 Å. The C(1)-O(1) bond length is 1.25 Å. The C(1)-O(2) bond length is 1.25 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(4) atom. The C(2)-C(3) bond length is 1.39 Å. The C(2)-C(4) bond length is 1.40 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(2), one C(3), and one C(5) atom. The C(4)-C(5) bond length is 1.51 Å. In the fifth C site, C(5) is bonded in a distorted bent 120 degrees geometry to one C(4), one O(3), and one O(4) atom. The C(5)-O(3) bond length is 1.25 Å. The C(5)-O(4) bond length is 1.26 Å. In the sixth C site, C(6) is bonded in a distorted bent 120 degrees geometry to one C(7), one O(5), and one O(6) atom. The C(6)-C(7) bond length is 1.51 Å. The C(6)-O(5) bond length is 1.26 Å. The C(6)-O(6) bond length is 1.24 Å. In the seventh C site, C(7) is bonded in a trigonal planar geometry to one C(6), one C(8), and one C(9) atom. The C(7)-C(8) bond length is 1.39 Å. The C(7)-C(9) bond length is 1.40 Å. In the eighth C site, C(8) is bonded in a single-bond geometry to one C(7), one C(9), and one H(3) atom. The C(8)-C(9) bond length is 1.39 Å. The C(8)-H(3) bond length is 0.93 Å. In the ninth C site, C(9) is bonded in a trigonal planar geometry to one C(10), one C(7), and one C(8) atom. The C(9)-C(10) bond length is 1.51 Å. In the tenth C site, C(10) is bonded in a distorted bent 120 degrees geometry to one C(9), one O(7), and one O(8) atom. The C(10)-O(7) bond length is 1.24 Å. The C(10)-O(8) bond length is 1.27 Å. There are three inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one O(9) atom. The H(1)-O(9) bond length is 0.98 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(8) atom. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Mg(1) and one C(1) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one Mg(2) and one C(1) atom. In the third O site, O(3) is bonded in a bent 120 degrees geometry to one Mg(3) and one C(5) atom. In the fourth O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Mg(2) and one C(5) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Mg(2), one Mg(3), and one C(6) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Mg(1) and one C(6) atom. In the seventh O site, O(7) is bonded in a distorted single-bond geometry to one Mg(1) and one C(10) atom. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Mg(1), one Mg(2), and one C(10) atom. In the ninth O site, O(9) is bonded to one Mg(1), one Mg(2), one Mg(3), and one H(1) atom to form distorted corner-sharing OMg3H tetrahedra. Linkers: 4 [O]C(=O)c1cc(C([O])=O)c(C([O])=O)cc1C([O])=O. Metal clusters: 5 [Mg]. The MOF has largest included sphere 6.88 A, density 1.18 g/cm3, surface area 3326.44 m2/g, accessible volume 0.41 cm3/g