CuC2N4H4O crystallizes in the trigonal P3_221 space group. Cu(1) is bonded in a square co-planar geometry to one N(1), one N(2), one N(3), and one O(1) atom. The Cu(1)-N(1) bond length is 1.98 Å. The Cu(1)-N(2) bond length is 1.99 Å. The Cu(1)-N(3) bond length is 1.98 Å. The Cu(1)-O(1) bond length is 2.01 Å. There are two inequivalent C sites. In the first C site, C(1) is bonded in a trigonal planar geometry to one N(2), one N(3), and one N(4) atom. The C(1)-N(2) bond length is 1.32 Å. The C(1)-N(3) bond length is 1.37 Å. The C(1)-N(4) bond length is 1.36 Å. In the second C site, C(2) is bonded in a trigonal planar geometry to one N(1), one N(3), and one H(1) atom. The C(2)-N(1) bond length is 1.32 Å. The C(2)-N(3) bond length is 1.35 Å. The C(2)-H(1) bond length is 0.93 Å. There are four inequivalent N sites. In the first N site, N(1) is bonded in a distorted trigonal planar geometry to one Cu(1), one C(2), and one N(2) atom. The N(1)-N(2) bond length is 1.38 Å. In the second N site, N(2) is bonded in a distorted trigonal planar geometry to one Cu(1), one C(1), and one N(1) atom. In the third N site, N(3) is bonded in a trigonal planar geometry to one Cu(1), one C(1), and one C(2) atom. In the fourth N site, N(4) is bonded in a distorted trigonal planar geometry to one C(1), one H(2), and one H(3) atom. The N(4)-H(2) bond length is 0.86 Å. The N(4)-H(3) bond length is 0.86 Å. There are four inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one C(2) atom. In the second H site, H(2) is bonded in a single-bond geometry to one N(4) atom. In the third H site, H(3) is bonded in a single-bond geometry to one N(4) atom. In the fourth H site, H(4) is bonded in a single-bond geometry to one O(1) atom. The H(4)-O(1) bond length is 0.82 Å. O(1) is bonded in a water-like geometry to one Cu(1) and one H(4) atom. Linkers: 3 NC1=NN=C[N]1 ,1 NC1=NC=N[N]1 ,1 NC1=[N]=CN=N1 ,1 NC1=N[N]C=N1. Metal clusters: 3 O[Cu]1=NN=[Cu](O)N=N1. The MOF has largest included sphere 6.83 A, density 1.26 g/cm3, surface area 3582.59 m2/g, accessible volume 0.47 cm3/g