NiC5H5O4 crystallizes in the trigonal R-3 space group. Ni(1) is bonded to one O(2), one O(4), two equivalent O(1), and two equivalent O(3) atoms to form NiO6 octahedra that share  a cornercorner with one C(5)H3O tetrahedra and edges with two equivalent Ni(1)O6 octahedra. The Ni(1)-O(2) bond length is 2.03 Å. The Ni(1)-O(4) bond length is 2.18 Å. There is one shorter (2.01 Å) and one longer (2.04 Å) Ni(1)-O(1) bond length. There is one shorter (2.02 Å) and one longer (2.05 Å) Ni(1)-O(3) bond length. There are five inequivalent C sites. In the first C site, C(5) is bonded to one H(3), one H(4), one H(5), and one O(4) atom to form CH3O tetrahedra that share  a cornercorner with one Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles are 57°. The C(5)-H(3) bond length is 1.09 Å. The C(5)-H(4) bond length is 1.10 Å. The C(5)-H(5) bond length is 1.10 Å. The C(5)-O(4) bond length is 1.45 Å. In the second C site, C(1) is bonded in a distorted trigonal planar geometry to one C(3), one C(4), and one H(1) atom. The C(1)-C(3) bond length is 1.40 Å. The C(1)-C(4) bond length is 1.40 Å. The C(1)-H(1) bond length is 1.09 Å. In the third C site, C(2) is bonded in a distorted bent 120 degrees geometry to one C(3), one O(1), and one O(2) atom. The C(2)-C(3) bond length is 1.49 Å. The C(2)-O(1) bond length is 1.29 Å. The C(2)-O(2) bond length is 1.27 Å. In the fourth C site, C(4) is bonded in a distorted single-bond geometry to one C(1), one C(3), and one O(3) atom. The C(4)-C(3) bond length is 1.43 Å. The C(4)-O(3) bond length is 1.35 Å. In the fifth C site, C(3) is bonded in a trigonal planar geometry to one C(1), one C(2), and one C(4) atom. There are five inequivalent H sites. In the first H site, H(4) is bonded in a single-bond geometry to one C(5) atom. In the second H site, H(5) is bonded in a single-bond geometry to one C(5) atom. In the third H site, H(1) is bonded in a single-bond geometry to one C(1) atom. In the fourth H site, H(2) is bonded in a single-bond geometry to one O(4) atom. The H(2)-O(4) bond length is 0.98 Å. In the fifth H site, H(3) is bonded in a single-bond geometry to one C(5) atom. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to two equivalent Ni(1) and one C(2) atom. In the second O site, O(2) is bonded in a bent 120 degrees geometry to one Ni(1) and one C(2) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to two equivalent Ni(1) and one C(4) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Ni(1), one C(5), and one H(2) atom. Linkers: 3 [O]C(=O)c1cc([O])c(C([O])=O)cc1[O]. Metal clusters: 6 [Ni]. The MOF has largest included sphere 7.37 A, density 1.43 g/cm3, surface area 3053.26 m2/g, accessible volume 0.37 cm3/g