NiC4HO3 crystallizes in the trigonal R3m space group. Ni(1) is bonded to one O(1), two equivalent O(2), and two equivalent O(3) atoms to form edge-sharing NiO5 square pyramids. The Ni(1)-O(1) bond length is 2.00 Å. There is one shorter (1.91 Å) and one longer (2.02 Å) Ni(1)-O(2) bond length. There is one shorter (1.98 Å) and one longer (2.13 Å) Ni(1)-O(3) bond length. There are five inequivalent C sites. In the first C site, C(1) is bonded in a distorted trigonal planar geometry to two equivalent C(2) and one H(1) atom. Both C(1)-C(2) bond lengths are 1.39 Å. The C(1)-H(1) bond length is 0.83 Å. In the second C site, C(2) is bonded in a trigonal planar geometry to one C(1), one C(4), and one C(5) atom. The C(2)-C(4) bond length is 1.49 Å. The C(2)-C(5) bond length is 1.50 Å. In the third C site, C(3) is bonded in a distorted trigonal planar geometry to two equivalent C(5) and one H(2) atom. Both C(3)-C(5) bond lengths are 1.39 Å. The C(3)-H(2) bond length is 1.04 Å. In the fourth C site, C(4) is bonded in a distorted bent 120 degrees geometry to one C(2), one O(1), and one O(2) atom. The C(4)-O(1) bond length is 1.34 Å. The C(4)-O(2) bond length is 1.30 Å. In the fifth C site, C(5) is bonded in a single-bond geometry to one C(2), one C(3), and one O(3) atom. The C(5)-O(3) bond length is 1.27 Å. 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(3) atom. There are three inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one Ni(1) and one C(4) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to two equivalent Ni(1) and one C(4) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to two equivalent Ni(1) and one C(5) atom. Linkers: 3 [O]C(=O)[C]1[CH][C](C([O])=O)C(=O)[CH]C1=O. Metal clusters: 6 [Ni]. The MOF has largest included sphere 11.05 A, density 1.20 g/cm3, surface area 2532.58 m2/g, accessible volume 0.52 cm3/g