CsC4N2H4O3I crystallizes in the triclinic P-1 space group. The structure consists of two hydriodic acid atoms inside a CsC4N2H4O3 framework. In the CsC4N2H4O3 framework, Cs(1) is bonded in a 5-coordinate geometry to one O(1), two equivalent O(2), and two equivalent O(3) atoms. The Cs(1)-O(1) bond length is 3.16 Å. There is one shorter (3.13 Å) and one longer (3.17 Å) Cs(1)-O(2) bond length. There is one shorter (3.10 Å) and one longer (3.40 Å) Cs(1)-O(3) bond length. There are four inequivalent C sites. In the first C site, C(1) is bonded in a distorted trigonal planar geometry to one C(3), one N(2), and one O(1) atom. The C(1)-C(3) bond length is 1.50 Å. The C(1)-N(2) bond length is 1.36 Å. The C(1)-O(1) bond length is 1.24 Å. In the second C site, C(2) is bonded in a distorted trigonal planar geometry to one C(3), one N(1), and one O(2) atom. The C(2)-C(3) bond length is 1.50 Å. The C(2)-N(1) bond length is 1.38 Å. The C(2)-O(2) bond length is 1.23 Å. In the third C site, C(3) is bonded in a distorted water-like geometry to one C(1), one C(2), one H(1), and one H(2) atom. The C(3)-H(1) bond length is 1.11 Å. The C(3)-H(2) bond length is 1.10 Å. In the fourth C site, C(4) is bonded in a trigonal planar geometry to one N(1), one N(2), and one O(3) atom. The C(4)-N(1) bond length is 1.38 Å. The C(4)-N(2) bond length is 1.39 Å. The C(4)-O(3) bond length is 1.23 Å. There are two inequivalent N sites. In the first N site, N(1) is bonded in a trigonal planar geometry to one C(2), one C(4), and one H(3) atom. The N(1)-H(3) bond length is 1.04 Å. In the second N site, N(2) is bonded in a trigonal planar geometry to one C(1), one C(4), and one H(4) atom. The N(2)-H(4) bond length is 1.04 Å. There are four inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one C(3) atom. In the second H site, H(2) is bonded in a single-bond geometry to one C(3) atom. In the third H site, H(3) is bonded in a single-bond geometry to one N(1) atom. In the fourth H site, H(4) is bonded in a single-bond geometry to one N(2) atom. There are three inequivalent O sites. In the first O site, O(1) is bonded in a single-bond geometry to one Cs(1) and one C(1) atom. In the second O site, O(2) is bonded in a single-bond geometry to two equivalent Cs(1) and one C(2) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to two equivalent Cs(1) and one C(4) atom. Linkers: 2 O=C1CC(=O)NC(=O)N1. Metal clusters: 2 [Cs]. The MOF has largest included sphere 1.96 A, density 2.78 g/cm3, surface area 2775.99 m2/g, accessible volume 0.10 cm3/g