Mg4P3H6(C2O7)4 crystallizes in the monoclinic C2/c space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(1), one O(13), one O(7), one O(9), and two equivalent O(11) atoms to form MgO6 octahedra that share  a cornercorner with one P(1)O4 tetrahedra and  an edgeedge with one Mg(1)O6 octahedra. The Mg(1)-O(1) bond length is 1.99 Å. The Mg(1)-O(13) bond length is 2.08 Å. The Mg(1)-O(7) bond length is 2.16 Å. The Mg(1)-O(9) bond length is 2.06 Å. There is one shorter (2.10 Å) and one longer (2.14 Å) Mg(1)-O(11) bond length. In the second Mg site, Mg(2) is bonded to one O(10), one O(12), one O(14), one O(2), one O(5), and one O(8) atom to form MgO6 octahedra that share  a cornercorner with one P(1)O4 tetrahedra and  a cornercorner with one P(2)O4 tetrahedra. The Mg(2)-O(10) bond length is 2.17 Å. The Mg(2)-O(12) bond length is 2.15 Å. The Mg(2)-O(14) bond length is 2.10 Å. The Mg(2)-O(2) bond length is 2.01 Å. The Mg(2)-O(5) bond length is 1.99 Å. The Mg(2)-O(8) bond length is 2.11 Å. There are four inequivalent C sites. In the first C site, C(1) is bonded in a distorted bent 120 degrees geometry to one O(7) and one O(8) atom. The C(1)-O(7) bond length is 1.27 Å. The C(1)-O(8) bond length is 1.24 Å. In the second C site, C(2) is bonded in a distorted bent 120 degrees geometry to one O(10) and one O(9) atom. The C(2)-O(10) bond length is 1.24 Å. The C(2)-O(9) bond length is 1.25 Å. In the third C site, C(3) is bonded in a distorted bent 120 degrees geometry to one O(11) and one O(12) atom. The C(3)-O(11) bond length is 1.26 Å. The C(3)-O(12) bond length is 1.23 Å. In the fourth C site, C(4) is bonded in a distorted bent 120 degrees geometry to one O(13) and one O(14) atom. The C(4)-O(13) bond length is 1.25 Å. The C(4)-O(14) bond length is 1.24 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra and  a cornercorner with one Mg(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 36-40°. The P(1)-O(1) bond length is 1.49 Å. The P(1)-O(2) bond length is 1.48 Å. The P(1)-O(3) bond length is 1.56 Å. The P(1)-O(4) bond length is 1.58 Å. In the second P site, P(2) is bonded to two equivalent O(5) and two equivalent O(6) atoms to form PO4 tetrahedra that share corners with two equivalent Mg(2)O6 octahedra. The corner-sharing octahedral tilt angles are 35°. Both P(2)-O(5) bond lengths are 1.46 Å. Both P(2)-O(6) bond lengths are 1.56 Å. There are three inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one O(3) atom. The H(1)-O(3) bond length is 0.82 Å. In the second H site, H(2) is bonded in a single-bond geometry to one O(4) atom. The H(2)-O(4) bond length is 0.82 Å. In the third H site, H(3) is bonded in a single-bond geometry to one O(6) atom. The H(3)-O(6) bond length is 0.82 Å. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Mg(1) and one P(1) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Mg(2) and one P(1) atom. In the third O site, O(3) is bonded in a water-like geometry to one P(1) and one H(1) atom. In the fourth O site, O(4) is bonded in a water-like geometry to one P(1) and one H(2) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Mg(2) and one P(2) atom. In the sixth O site, O(6) is bonded in a water-like geometry to one P(2) and one H(3) atom. In the seventh O site, O(7) is bonded in a bent 120 degrees geometry to one Mg(1) and one C(1) atom. In the eighth O site, O(8) is bonded in a bent 120 degrees geometry to one Mg(2) and one C(1) atom. In the ninth O site, O(9) is bonded in a bent 120 degrees geometry to one Mg(1) and one C(2) atom. In the tenth O site, O(10) is bonded in a bent 120 degrees geometry to one Mg(2) and one C(2) atom. In the eleventh O site, O(11) is bonded in a distorted trigonal planar geometry to two equivalent Mg(1) and one C(3) atom. In the twelfth O site, O(12) is bonded in a bent 120 degrees geometry to one Mg(2) and one C(3) atom. In the thirteenth O site, O(13) is bonded in a bent 120 degrees geometry to one Mg(1) and one C(4) atom. In the fourteenth O site, O(14) is bonded in a bent 120 degrees geometry to one Mg(2) and one C(4) atom. Linkers: 16 [O]C(=O)C([O])=O. Metal clusters: 16 [Mg]. The MOF has largest included sphere 4.36 A, density 1.36 g/cm3, surface area 3661.23 m2/g, accessible volume 0.36 cm3/g