NaPH5(C2O)3 crystallizes in the monoclinic C2/c space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to two equivalent O(1) and four equivalent O(2) atoms. Both Na(1)-O(1) bond lengths are 2.38 Å. There are two shorter (2.31 Å) and two longer (2.55 Å) Na(1)-O(2) bond lengths. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to two equivalent O(3) and four equivalent O(1) atoms. Both Na(2)-O(3) bond lengths are 2.67 Å. There are two shorter (2.29 Å) and two longer (2.36 Å) Na(2)-O(1) bond lengths. There are six inequivalent C sites. In the first C site, C(3) is bonded in a distorted trigonal planar geometry to one C(1), one C(4), and one H(4) atom. The C(3)-C(1) bond length is 1.40 Å. The C(3)-C(4) bond length is 1.39 Å. The C(3)-H(4) bond length is 1.09 Å. In the second C site, C(4) is bonded in a distorted trigonal planar geometry to one C(3), one C(6), and one H(3) atom. The C(4)-C(6) bond length is 1.41 Å. The C(4)-H(3) bond length is 1.09 Å. In the third C site, C(5) is bonded in a distorted trigonal planar geometry to one C(2), one C(6), and one H(1) atom. The C(5)-C(2) bond length is 1.39 Å. The C(5)-C(6) bond length is 1.41 Å. The C(5)-H(1) bond length is 1.09 Å. In the fourth C site, C(6) is bonded in a trigonal planar geometry to one C(4), one C(5), and one C(6) atom. The C(6)-C(6) bond length is 1.48 Å. In the fifth C site, C(2) is bonded in a distorted single-bond geometry to one C(1), one C(5), and one H(2) atom. The C(2)-C(1) bond length is 1.40 Å. The C(2)-H(2) bond length is 1.09 Å. In the sixth C site, C(1) is bonded in a trigonal planar geometry to one C(2), one C(3), and one P(1) atom. The C(1)-P(1) bond length is 1.80 Å. P(1) is bonded in a tetrahedral geometry to one C(1), one O(1), one O(2), and one O(3) atom. The P(1)-O(1) bond length is 1.52 Å. The P(1)-O(2) bond length is 1.53 Å. The P(1)-O(3) bond length is 1.59 Å. There are five inequivalent H sites. In the first H site, H(5) is bonded in a linear geometry to one O(2) and one O(3) atom. The H(5)-O(2) bond length is 1.49 Å. The H(5)-O(3) bond length is 1.04 Å. In the second H site, H(1) is bonded in a single-bond geometry to one C(5) atom. In the third H site, H(2) is bonded in a single-bond geometry to one C(2) atom. In the fourth H site, H(3) is bonded in a single-bond geometry to one C(4) atom. In the fifth H site, H(4) is bonded in a single-bond geometry to one C(3) atom. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted see-saw-like geometry to one Na(1), two equivalent Na(2), and one P(1) atom. In the second O site, O(2) is bonded to two equivalent Na(1), one P(1), and one H(5) atom to form a mixture of distorted edge and corner-sharing ONa2PH trigonal pyramids. In the third O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Na(2), one P(1), and one H(5) atom. Linkers: 2 [O]P(=O)(O)c1ccc(-c2ccc(P([O])(=O)O)cc2)cc1 ,2 [O]P([O])c1[c]cc(-c2ccc(P([O])(=O)O)cc2)cc1. Metal clusters: 4 [Na]. The MOF has largest included sphere 1.40 A, density 1.82 g/cm3, surface area 3220.56 m2/g, accessible volume 0.08 cm3/g