Coordination polymers self-assembling from cadmium(II) ions and flexible pyridine-based bridging ligands

This paper describes coordination polymers assembled from cadmium nitrate and flexible bridging ligands, py-X-py (py = 4-pyridyl, 1a: X = CH2, 1b: X = C(=CH2), 1c: X = CH2CH2). The X-ray structure analysis of these complexes showed that their infinite topologies are quite different from each other, despite the structural similarity of ligands 1a-1c. Upon treatment with Cd(NO3)(2), 1a gave an infinite two-dimensional sheet structure with a stoichiometry of ML2 (M and L denote metal and ligand, respectively). Ligand 1b also afforded an infinite polymer possessing the same ML2 composition. However, the polymer structure is characterized by one-dimensionally bounded macrocyclic frameworks where adjacent Cd ions are linked by two ligand molecules. Interestingly, ligand 1c gave an infinite polymer of M2L3 composition whose structure was shown to be a unique one-dimensional framework having macrocyclic frameworks (M2L2) linked together by the third L molecules.