Syntheses and crystal structures of two self-assembled dizinc(II) helicates with novel hydrazone linked polypyridyl ligands

The rationally designed polydentate ligands, L and L, based on the pyridinyl moiety and the hydrazone fragment have been synthesized to coordinate zinc(II) ions. We utilize pyridine as a rigid core connecting two bipyridines as ligand building blocks with a hydrozone linker for the L. The L has a reversed design in which a bipyridine was used as a hinging-available building block of the ligand core, connecting two pyridazine arms with a hydrazone linker. Two novel helical dizinc(II) complexes were obtained by the reaction of L and L with zinc(II) perchlorate in acetonitrile. The structures of both helicates were confirmed by X-ray diffractometry. Single-stranded helicate ZnL contains two zinc ions bridged by an oxygen atom. Except for the L ligand, no other bridging species were found between the two zinc ions in the double-stranded helicate ZnL. The self-assembling process of helicate ZnL in solution state was studied by UV–Vis spectrometric titration experiments. The stepwise formation constants imply a slightly positive cooperative behavior for the formation of helicates.