NiC5N5H5O3 crystallizes in the monoclinic C2/c space group. Ni(1) is bonded to one N(1), one N(2), two equivalent N(3), one O(1), and one O(3) atom to form edge-sharing NiN4O2 octahedra. The Ni(1)-N(1) bond length is 2.06 Å. The Ni(1)-N(2) bond length is 2.09 Å. There is one shorter (2.08 Å) and one longer (2.10 Å) Ni(1)-N(3) bond length. The Ni(1)-O(1) bond length is 2.10 Å. The Ni(1)-O(3) bond length is 2.07 Å. There are five inequivalent C sites. In the first C site, C(1) is bonded in a distorted bent 120 degrees geometry to one C(2), one O(1), and one O(2) atom. The C(1)-C(2) bond length is 1.50 Å. The C(1)-O(1) bond length is 1.29 Å. The C(1)-O(2) bond length is 1.24 Å. In the second C site, C(2) is bonded in a distorted trigonal planar geometry to one C(1), one C(3), and one N(1) atom. The C(2)-C(3) bond length is 1.39 Å. The C(2)-N(1) bond length is 1.35 Å. In the third C site, C(3) is bonded in a distorted bent 120 degrees geometry to one C(2), one N(2), and one H(3) atom. The C(3)-N(2) bond length is 1.34 Å. The C(3)-H(3) bond length is 1.09 Å. In the fourth C site, C(4) is bonded in a distorted bent 120 degrees geometry to one N(1) and one H(4) atom. The C(4)-N(1) bond length is 1.34 Å. The C(4)-H(4) bond length is 1.09 Å. In the fifth C site, C(5) is bonded in a distorted trigonal planar geometry to one N(2) and one H(5) atom. The C(5)-N(2) bond length is 1.35 Å. The C(5)-H(5) bond length is 1.09 Å. There are five inequivalent N sites. In the first N site, N(1) is bonded in a trigonal planar geometry to one Ni(1), one C(2), and one C(4) atom. In the second N site, N(2) is bonded in a trigonal planar geometry to one Ni(1), one C(3), and one C(5) atom. In the third N site, N(3) is bonded in a distorted trigonal planar geometry to two equivalent Ni(1) and one N(4) atom. The N(3)-N(4) bond length is 1.21 Å. In the fourth N site, N(4) is bonded in a linear geometry to one N(3) and one N(5) atom. The N(4)-N(5) bond length is 1.17 Å. In the fifth N site, N(5) is bonded in a single-bond geometry to one N(4) atom. There are five inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one O(2) and one O(3) atom. The H(1)-O(2) bond length is 1.70 Å. The H(1)-O(3) bond length is 0.99 Å. In the second H site, H(2) is bonded in a single-bond geometry to one O(1) and one O(3) atom. The H(2)-O(1) bond length is 1.73 Å. The H(2)-O(3) bond length is 0.99 Å. In the third H site, H(3) is bonded in a single-bond geometry to one C(3) atom. In the fourth H site, H(4) is bonded in a single-bond geometry to one C(4) atom. In the fifth H site, H(5) is bonded in a single-bond geometry to one C(5) atom. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Ni(1), one C(1), and one H(2) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one C(1) and one H(1) atom. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Ni(1), one H(1), and one H(2) atom. Linkers: 4 [O]C(=O)c1cnccn1. Metal clusters: 4 [Ni]. The MOF has largest included sphere 1.68 A, density 2.06 g/cm3, surface area 3516.79 m2/g, accessible volume 0.09 cm3/g