CdC3N3H2O2 crystallizes in the orthorhombic Pnna space group. There are two inequivalent Cd sites. In the first Cd site, Cd(1) is bonded to two equivalent N(1), two equivalent N(3), and two equivalent O(1) atoms to form corner-sharing CdN4O2 octahedra. Both Cd(1)-N(1) bond lengths are 2.41 Å. Both Cd(1)-N(3) bond lengths are 2.32 Å. Both Cd(1)-O(1) bond lengths are 2.43 Å. In the second Cd site, Cd(2) is bonded to two equivalent N(2), two equivalent O(1), and two equivalent O(2) atoms to form distorted corner-sharing CdN2O4 pentagonal pyramids. The corner-sharing octahedral tilt angles are 61°. Both Cd(2)-N(2) bond lengths are 2.28 Å. Both Cd(2)-O(1) bond lengths are 2.36 Å. Both Cd(2)-O(2) bond lengths are 2.32 Å. There are three inequivalent C sites. In the first C site, C(2) is bonded in a trigonal planar geometry to one N(2), one N(3), and one H(2) atom. The C(2)-N(2) bond length is 1.33 Å. The C(2)-N(3) bond length is 1.35 Å. The C(2)-H(2) bond length is 1.09 Å. In the second C site, C(3) is bonded in a distorted bent 120 degrees geometry to one O(1) and one O(2) atom. The C(3)-O(1) bond length is 1.28 Å. The C(3)-O(2) bond length is 1.25 Å. In the third C site, C(1) is bonded in a trigonal planar geometry to one N(1), one N(3), and one H(1) atom. The C(1)-N(1) bond length is 1.33 Å. The C(1)-N(3) bond length is 1.36 Å. The C(1)-H(1) bond length is 1.08 Å. There are three inequivalent N sites. In the first N site, N(3) is bonded in a distorted trigonal planar geometry to one Cd(1), one C(1), and one C(2) atom. In the second N site, N(1) is bonded in a distorted trigonal planar geometry to one Cd(1), one C(1), and one N(2) atom. The N(1)-N(2) bond length is 1.38 Å. In the third N site, N(2) is bonded in a distorted trigonal planar geometry to one Cd(2), one C(2), and one N(1) atom. There are two inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one C(1) atom. In the second H site, H(2) is bonded in a single-bond geometry to one C(2) atom. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Cd(1), one Cd(2), and one C(3) atom. In the second O site, O(2) is bonded in a bent 120 degrees geometry to one Cd(2) and one C(3) atom. Linkers: 3 [O]C(=O)C([O])=O ,8 C1=NC=N[N]1. Metal clusters: 8 [Cd]. The MOF has largest included sphere 2.82 A, density 2.49 g/cm3, surface area 2805.05 m2/g, accessible volume 0.13 cm3/g