Versatile 2,5-Pyridinedicarboxylate in Linking Transition-Metal Atoms into 1D and 2D Coordination Polymers and Concomitant Polymorphs

A novel two-dimensional cobalt(II) complex composed of one-dimensional twisted pair-like chains: poly[[tetraaquabis(μ3-pyridine-2,5-dicarboxylato-κ(4)N,O(2):O(5):O(5'))dicobalt(II)] dihydrate]

A novel neutral polymer, {[Co2(C7H3NO4)2(H2O)4]·2H2O}n, was hydrothermally synthesized using pyridine-2,5-dicarboxylate (2,5-PDC(2-)) as the organic linker. It features a two-dimensional layer structure constructed from one-dimensional {[Co(2,5-PDC)2](2-)}n chains interlinked by [Co(H2O)4](+) units. The two Co(II) cations occupy special positions, sitting on inversion centres. Each 2,5-PDC(2-) anion chelates to one Co(II) cation via the pyridine N atom and an O atom of the adjacent carboxylate group, and links to two other Co(II) cations in a bridging mode via the O atoms of the other carboxylate group. In this way, the 2,5-PDC(2-) ligand connects three neighbouring Co(II) centres to form a two-dimensional network. The two-dimensional undulating layers are linked by extensive hydrogen bonds to form a three-dimensional supramolecular structure, with the uncoordinated solvent molecules occupying the interlamellar region.