U3P4H8(C2O7)2 crystallizes in the orthorhombic Cmc2_1 space group. There are two inequivalent U sites. In the first U site, U(1) is bonded in a 4-coordinate geometry to one O(1), one O(2), one O(4), and one O(6) atom. The U(1)-O(1) bond length is 2.31 Å. The U(1)-O(2) bond length is 2.35 Å. The U(1)-O(4) bond length is 2.38 Å. The U(1)-O(6) bond length is 2.36 Å. In the second U site, U(2) is bonded in a 4-coordinate geometry to two equivalent O(3) and two equivalent O(5) atoms. Both U(2)-O(3) bond lengths are 2.34 Å. Both U(2)-O(5) bond lengths are 2.31 Å. There are two inequivalent C sites. In the first C site, C(1) is bonded in a distorted tetrahedral geometry to one C(2), one P(1), one P(2), and one O(7) atom. The C(1)-C(2) bond length is 1.51 Å. The C(1)-P(1) bond length is 1.80 Å. The C(1)-P(2) bond length is 1.84 Å. The C(1)-O(7) bond length is 1.47 Å. In the second C site, C(2) is bonded in a trigonal non-coplanar geometry to one C(1); one H(3); and two equivalent H(1,2) atoms. The C(2)-H(3) bond length is 0.96 Å. Both C(2)-H(1,2) bond lengths are 0.96 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one C(1), one O(2), one O(3), and one O(6) atom to form corner-sharing PCO3 tetrahedra. The P(1)-O(2) bond length is 1.51 Å. The P(1)-O(3) bond length is 1.53 Å. The P(1)-O(6) bond length is 1.53 Å. In the second P site, P(2) is bonded to one C(1), one O(1), one O(4), and one O(5) atom to form corner-sharing PCO3 tetrahedra. The P(2)-O(1) bond length is 1.50 Å. The P(2)-O(4) bond length is 1.53 Å. The P(2)-O(5) bond length is 1.54 Å. There are three inequivalent H sites. In the first H site, H(1,2) is bonded in a single-bond geometry to one C(2) atom. In the second H site, H(3) is bonded in a single-bond geometry to one C(2) atom. In the third H site, H(4) is bonded in a single-bond geometry to one O(7) atom. The H(4)-O(7) bond length is 0.82 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to one U(1) and one P(2) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one U(1) and one P(1) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to one U(2) and one P(1) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to one U(1) and one P(2) atom. In the fifth O site, O(5) is bonded in a distorted single-bond geometry to one U(2) and one P(2) atom. In the sixth O site, O(6) is bonded in a distorted bent 150 degrees geometry to one U(1) and one P(1) atom. In the seventh O site, O(7) is bonded in a water-like geometry to one C(1) and one H(4) atom. Linkers: 4 CC(O)(P([O])([O])=O)P([O])([O])=O. Metal clusters: 6 [U]. The MOF has largest included sphere 6.82 A, density 2.34 g/cm3, surface area 1703.69 m2/g, accessible volume 0.24 cm3/g