CsPH4(CO3)2 crystallizes in the orthorhombic P2_12_12_1 space group. Cs(1) is bonded in a 10-coordinate geometry to one H(1), one O(1), one O(2), one O(3), one O(6), two equivalent O(4), and three equivalent O(5) atoms. The Cs(1)-H(1) bond length is 3.19 Å. The Cs(1)-O(1) bond length is 3.13 Å. The Cs(1)-O(2) bond length is 3.13 Å. The Cs(1)-O(3) bond length is 3.48 Å. The Cs(1)-O(6) bond length is 3.12 Å. There is one shorter (3.21 Å) and one longer (3.48 Å) Cs(1)-O(4) bond length. There are a spread of Cs(1)-O(5) bond distances ranging from 3.04-3.29 Å. There are two inequivalent C sites. In the first C site, C(1) is bonded in a 4-coordinate geometry to one C(2), one P(1), one H(2), and one O(4) atom. The C(1)-C(2) bond length is 1.52 Å. The C(1)-P(1) bond length is 1.87 Å. The C(1)-H(2) bond length is 1.10 Å. The C(1)-O(4) bond length is 1.42 Å. In the second C site, C(2) is bonded in a distorted bent 120 degrees geometry to one C(1), one O(5), and one O(6) atom. The C(2)-O(5) bond length is 1.24 Å. The C(2)-O(6) bond length is 1.31 Å. P(1) is bonded in a distorted 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 1.58 Å. The P(1)-O(3) bond length is 1.53 Å. There are four inequivalent H sites. In the first H site, H(1) is bonded in a distorted linear geometry to one Cs(1), one O(2), and one O(3) atom. The H(1)-O(2) bond length is 1.03 Å. The H(1)-O(3) bond length is 1.52 Å. In the second H site, H(2) is bonded in a single-bond geometry to one C(1) atom. In the third H site, H(3) is bonded in a distorted linear geometry to one O(3) and one O(4) atom. The H(3)-O(3) bond length is 1.66 Å. The H(3)-O(4) bond length is 1.00 Å. In the fourth H site, H(4) is bonded in a linear geometry to one O(1) and one O(6) atom. The H(4)-O(1) bond length is 1.40 Å. The H(4)-O(6) bond length is 1.07 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one Cs(1), one P(1), and one H(4) atom. In the second O site, O(2) is bonded in a bent 120 degrees geometry to one Cs(1), one P(1), and one H(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Cs(1), one P(1), one H(1), and one H(3) atom. In the fourth O site, O(4) is bonded in a water-like geometry to two equivalent Cs(1), one C(1), and one H(3) atom. In the fifth O site, O(5) is bonded in a single-bond geometry to three equivalent Cs(1) and one C(2) atom. In the sixth O site, O(6) is bonded in a bent 120 degrees geometry to one Cs(1), one C(2), and one H(4) atom. Linkers: 4 [O]P(=O)(O)[C@H](O)C(=O)O. Metal clusters: 4 [Cs]. The MOF has largest included sphere 1.87 A, density 2.73 g/cm3, surface area 2521.50 m2/g, accessible volume 0.06 cm3/g