CsC2PN3H3O4 crystallizes in the monoclinic P2_1/c space group. Cs(1) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. There is one shorter (3.09 Å) and one longer (3.25 Å) Cs(1)-O(1) bond length. There is one shorter (3.06 Å) and one longer (3.33 Å) Cs(1)-O(2) bond length. There is one shorter (3.18 Å) and one longer (3.51 Å) Cs(1)-O(3) bond length. There is one shorter (3.12 Å) and one longer (3.30 Å) Cs(1)-O(4) bond length. There are two inequivalent C sites. In the first C site, C(1) is bonded in a trigonal planar geometry to one N(1), one N(2), and one O(1) atom. The C(1)-N(1) bond length is 1.35 Å. The C(1)-N(2) bond length is 1.37 Å. The C(1)-O(1) bond length is 1.26 Å. In the second C site, C(2) is bonded in a trigonal planar geometry to one N(2), one N(3), and one O(2) atom. The C(2)-N(2) bond length is 1.39 Å. The C(2)-N(3) bond length is 1.36 Å. The C(2)-O(2) bond length is 1.25 Å. P(1) is bonded in a tetrahedral geometry to one N(1), one N(3), one O(3), and one O(4) atom. The P(1)-N(1) bond length is 1.70 Å. The P(1)-N(3) bond length is 1.69 Å. The P(1)-O(3) bond length is 1.50 Å. The P(1)-O(4) bond length is 1.51 Å. There are three inequivalent N sites. In the first N site, N(2) is bonded in a trigonal planar geometry to one C(1), one C(2), and one H(2) atom. The N(2)-H(2) bond length is 1.05 Å. In the second N site, N(3) is bonded in a trigonal planar geometry to one C(2), one P(1), and one H(3) atom. The N(3)-H(3) bond length is 1.05 Å. In the third N site, N(1) is bonded in a trigonal planar geometry to one C(1), one P(1), and one H(1) atom. The N(1)-H(1) bond length is 1.05 Å. There are three inequivalent H sites. In the first H site, H(1) is bonded in a distorted single-bond geometry to one N(1) atom. In the second H site, H(2) is bonded in a single-bond geometry to one N(2) atom. In the third H site, H(3) is bonded in a distorted linear geometry to one N(3) and one O(4) atom. The H(3)-O(4) bond length is 1.67 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to two equivalent Cs(1) and one C(1) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to two equivalent Cs(1) and one C(2) atom. In the third O site, O(3) is bonded in a single-bond geometry to two equivalent Cs(1) and one P(1) atom. In the fourth O site, O(4) is bonded in a 1-coordinate geometry to two equivalent Cs(1), one P(1), and one H(3) atom. Linkers: 4 [O]P1(=O)NC(=O)NC(=O)N1. Metal clusters: 4 [Cs]. The MOF has largest included sphere 2.44 A, density 2.60 g/cm3, surface area 2673.20 m2/g, accessible volume 0.12 cm3/g