Anion dependent structural diversity in cobalt(II) complexes of 4,4′-bipyridine-N,N′-dioxide

Five cobalt(II) complexes with 4,4'-bipyridine-N, N'-dioxide have been prepared and characterised. Their topology and dimensionality depend on the counteranion used: for Br- and Cl- the structures are layered inorganic/organic salts; I- forms a 3D supramolecular network while both NO3- and SO42- induce the formation of interdigitated layer structures (with different coordination spheres) with a hydrophilic region between the Co(II) ions. The nitrate structure undergoes a reversible order-disorder phase transition at ca. 162 K. In all five complexes, pi center dot center dot center dot pi interactions are present between the bpdo molecules, possibly providing a directing force for the formation of these structures.