Lesego J. Moitsheki

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, π⋯π interactions are present between the bpdo molecules, possibly providing a directing force for the formation of these structures.

Solid State Transformations in Crystalline Salts

Two examples are described of reactions which proceed in the crystalline state. In the first, a metal-organic salt CoH2O6X2 ⋅2bpdo ⋅2H2O X = Br − , Cl − transforms at room temperature into a coordination polymer CoX2bpdoH2O2 ⋅H2O with different connectivity. The process can be followed by powder x-ray diffraction. In the second example, we observed sublimation/dissociation and recrystallisation under ambient pressure when a single crystal of 4-(1-hydroxy-1,2-diphenylethyl)pyridinium chloride was heated and the pure organic moiety crystallized on the mother crystal surface providing an excellent example of molecular structure – macroscopical property relationship which can be explained by partial isostructurality. Under similar conditions the nitrate salt of the same compound, 4-(1-hydroxy-1,2-diphenylethyl)pyridinium nitrate sublimed and recrystallised without dissociation. The two crystal structure of the salts are isostructural but the Hirshfeld surface analysis shows significant differences between the intermolecular interactions which can explain the different thermal behavior of them in the crystalline phase while the computational studies explained their behavior in gas phase.

catena-Poly[[methano­ltrinitratothallium(III)]-μ-4,4′-bipyridine N,N′-dioxide]

The title compound, [Tl(NO3)3(C10H8N2O2)(CH4O)]n, has a one-dimensional zigzag chain with nitrate and methanol ligands disordered over two positions.