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Key indicators: single-crystal X-ray study; T = 295 K; mean (C-C) = 0.002 Å; disorder in main residue; R factor = 0.030; wR factor = 0.085; data-to-parameter ratio = 15.9.The hydrothermal reaction of cobalt nitrate with 4,4 0 -bipyridine and 3-nitrobenzoic acid lead to the formation of the title complex, [Co(C 7 H 4 NO 4 ) 2 (C 10 H 8 N 2 ) 2 ] n . In the crystal structure, the Co II atoms are coordinated by two terminal carboxylate anions and four 4,4 0 -bipyridine ligands within slightly distorted octahedra. The Co II atom and one of the two independent 4,4 0 -bipyridine ligands are located on a twofold rotation axis, while the second independent 4,4 0 -bipyridine molecule is located on a centre of inversion. One of the two rings of one 4,4 0 -bipyridine ligand is disordered over two orientations and was refined using a split model [occupancy ratio 0.68 (2):0.32 (2)]. The Co II atoms are connected by the 4,4 0 -bipyridine ligands into layers, which are located parallel to the ab plane. Related literature

The microwave solvothermal reaction of nickel nitrate with trimesic acid provided the title compound, [Ni3(BTC)2(H2O)12]n (BTC = benzene-1,3,5-tricarboxyl­ate anion, C9H3O6), which is a metal coordination polymer composed of one-dimensional zigzag chains. The crystal under investigation was ramecically twinned with an approximate twin domain ratio of 1:1. In the asymmetric unit, there are two types of Ni atoms. One of the NiO6 groups (2 symmetry) is coordinated to only one carboxyl­ate group and thus terminal, the other is bridging, forming the coordination polymer. The extended chains are connected by the organic BTC anions via μ 2-linkages. O—H⋯O hydrogen bonds and π–π inter­actions between the chains [centroid–centroid distance 3.58 (1) Å] induce the complex to mimic a three-dimensional structure.