Mg4P3H5(C2O7)4 crystallizes in the triclinic P1 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(13), one O(15), one O(17), one O(19), one O(2), and one O(24) atom to form MgO6 octahedra that share  a cornercorner with one P(1)O4 tetrahedra and  an edgeedge with one Mg(2)O6 octahedra. The Mg(1)-O(13) bond length is 2.09 Å. The Mg(1)-O(15) bond length is 2.13 Å. The Mg(1)-O(17) bond length is 2.09 Å. The Mg(1)-O(19) bond length is 2.11 Å. The Mg(1)-O(2) bond length is 1.95 Å. The Mg(1)-O(24) bond length is 2.09 Å. In the second Mg site, Mg(2) is bonded to one O(1), one O(17), one O(22), one O(24), one O(26), and one O(28) atom 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(2)-O(1) bond length is 1.98 Å. The Mg(2)-O(17) bond length is 2.06 Å. The Mg(2)-O(22) bond length is 2.09 Å. The Mg(2)-O(24) bond length is 2.16 Å. The Mg(2)-O(26) bond length is 2.15 Å. The Mg(2)-O(28) bond length is 2.08 Å. In the third Mg site, Mg(3) is bonded to one O(14), one O(16), one O(18), one O(20), one O(5), and one O(9) atom to form MgO6 octahedra that share  a cornercorner with one P(2)O4 tetrahedra and  a cornercorner with one P(3)O4 tetrahedra. The Mg(3)-O(14) bond length is 2.18 Å. The Mg(3)-O(16) bond length is 2.13 Å. The Mg(3)-O(18) bond length is 2.12 Å. The Mg(3)-O(20) bond length is 2.09 Å. The Mg(3)-O(5) bond length is 2.01 Å. The Mg(3)-O(9) bond length is 2.00 Å. In the fourth Mg site, Mg(4) is bonded to one O(10), one O(21), one O(23), one O(25), one O(27), and one O(6) atom to form MgO6 octahedra that share  a cornercorner with one P(2)O4 tetrahedra and  a cornercorner with one P(3)O4 tetrahedra. The Mg(4)-O(10) bond length is 2.03 Å. The Mg(4)-O(21) bond length is 2.09 Å. The Mg(4)-O(23) bond length is 2.24 Å. The Mg(4)-O(25) bond length is 2.10 Å. The Mg(4)-O(27) bond length is 2.11 Å. The Mg(4)-O(6) bond length is 1.97 Å. There are eight inequivalent C sites. In the first C site, C(1) is bonded in a distorted bent 120 degrees geometry to one O(13) and one O(14) atom. The C(1)-O(13) bond length is 1.25 Å. The C(1)-O(14) bond length is 1.23 Å. In the second C site, C(2) is bonded in a distorted bent 120 degrees geometry to one O(15) and one O(16) atom. The C(2)-O(15) bond length is 1.25 Å. The C(2)-O(16) bond length is 1.24 Å. In the third C site, C(3) is bonded in a distorted bent 120 degrees geometry to one O(17) and one O(18) atom. The C(3)-O(17) bond length is 1.27 Å. The C(3)-O(18) 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(19) and one O(20) atom. The C(4)-O(19) bond length is 1.24 Å. The C(4)-O(20) bond length is 1.25 Å. In the fifth C site, C(5) is bonded in a distorted bent 120 degrees geometry to one O(21) and one O(22) atom. The C(5)-O(21) bond length is 1.24 Å. The C(5)-O(22) bond length is 1.24 Å. In the sixth C site, C(6) is bonded in a distorted bent 120 degrees geometry to one O(23) and one O(24) atom. The C(6)-O(23) bond length is 1.23 Å. The C(6)-O(24) bond length is 1.26 Å. In the seventh C site, C(7) is bonded in a distorted bent 120 degrees geometry to one O(25) and one O(26) atom. The C(7)-O(25) bond length is 1.25 Å. The C(7)-O(26) bond length is 1.25 Å. In the eighth C site, C(8) is bonded in a distorted bent 120 degrees geometry to one O(27) and one O(28) atom. The C(8)-O(27) bond length is 1.23 Å. The C(8)-O(28) bond length is 1.26 Å. There are three 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 34-43°. The P(1)-O(1) bond length is 1.50 Å. The P(1)-O(2) bond length is 1.49 Å. The P(1)-O(3) bond length is 1.59 Å. The P(1)-O(4) bond length is 1.54 Å. In the second P site, P(2) is bonded to one O(5), one O(6), one O(7), and one O(8) atom to form PO4 tetrahedra that share  a cornercorner with one Mg(3)O6 octahedra and  a cornercorner with one Mg(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 33-44°. The P(2)-O(5) bond length is 1.50 Å. The P(2)-O(6) bond length is 1.49 Å. The P(2)-O(7) bond length is 1.52 Å. The P(2)-O(8) bond length is 1.63 Å. In the third P site, P(3) is bonded to one O(10), one O(11), one O(12), and one O(9) atom to form PO4 tetrahedra that share  a cornercorner with one Mg(3)O6 octahedra and  a cornercorner with one Mg(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 34-49°. The P(3)-O(10) bond length is 1.50 Å. The P(3)-O(11) bond length is 1.58 Å. The P(3)-O(12) bond length is 1.56 Å. The P(3)-O(9) bond length is 1.49 Å. There are five 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 distorted single-bond geometry to one O(4) and one O(7) atom. The H(2)-O(4) bond length is 0.82 Å. The H(2)-O(7) bond length is 1.67 Å. In the third H site, H(3) is bonded in a single-bond geometry to one O(8) atom. The H(3)-O(8) bond length is 0.82 Å. In the fourth H site, H(4) is bonded in a single-bond geometry to one O(11) atom. The H(4)-O(11) bond length is 0.82 Å. In the fifth H site, H(5) is bonded in a single-bond geometry to one O(12) atom. The H(5)-O(12) bond length is 0.82 Å. There are twenty-eight inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Mg(2) and one P(1) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Mg(1) 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 distorted bent 150 degrees geometry to one Mg(3) and one P(2) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Mg(4) and one P(2) atom. In the seventh O site, O(7) is bonded in a distorted bent 120 degrees geometry to one P(2) and one H(2) atom. In the eighth O site, O(8) is bonded in a distorted water-like geometry to one P(2) and one H(3) atom. In the ninth O site, O(9) is bonded in a bent 150 degrees geometry to one Mg(3) and one P(3) atom. In the tenth O site, O(10) is bonded in a bent 120 degrees geometry to one Mg(4) and one P(3) atom. In the eleventh O site, O(11) is bonded in a water-like geometry to one P(3) and one H(4) atom. In the twelfth O site, O(12) is bonded in a water-like geometry to one P(3) and one H(5) atom. In the thirteenth O site, O(13) is bonded in a bent 120 degrees geometry to one Mg(1) and one C(1) atom. In the fourteenth O site, O(14) is bonded in a bent 120 degrees geometry to one Mg(3) and one C(1) atom. In the fifteenth O site, O(15) is bonded in a bent 120 degrees geometry to one Mg(1) and one C(2) atom. In the sixteenth O site, O(16) is bonded in a bent 120 degrees geometry to one Mg(3) and one C(2) atom. In the seventeenth O site, O(17) is bonded in a distorted trigonal planar geometry to one Mg(1), one Mg(2), and one C(3) atom. In the eighteenth O site, O(18) is bonded in a bent 120 degrees geometry to one Mg(3) and one C(3) atom. In the nineteenth O site, O(19) is bonded in a bent 120 degrees geometry to one Mg(1) and one C(4) atom. In the twentieth O site, O(20) is bonded in a bent 120 degrees geometry to one Mg(3) and one C(4) atom. In the twenty-first O site, O(21) is bonded in a bent 120 degrees geometry to one Mg(4) and one C(5) atom. In the twenty-second O site, O(22) is bonded in a bent 120 degrees geometry to one Mg(2) and one C(5) atom. In the twenty-third O site, O(23) is bonded in a bent 120 degrees geometry to one Mg(4) and one C(6) atom. In the twenty-fourth O site, O(24) is bonded in a distorted trigonal planar geometry to one Mg(1), one Mg(2), and one C(6) atom. In the twenty-fifth O site, O(25) is bonded in a bent 120 degrees geometry to one Mg(4) and one C(7) atom. In the twenty-sixth O site, O(26) is bonded in a bent 120 degrees geometry to one Mg(2) and one C(7) atom. In the twenty-seventh O site, O(27) is bonded in a bent 120 degrees geometry to one Mg(4) and one C(8) atom. In the twenty-eighth O site, O(28) is bonded in a bent 120 degrees geometry to one Mg(2) and one C(8) atom. Linkers: 4 [O]C(=O)C([O])=O. Metal clusters: 4 [Mg]. The MOF has largest included sphere 4.54 A, density 1.46 g/cm3, surface area 3851.29 m2/g, accessible volume 0.27 cm3/g