From anion complexes to anion coordination polymers (ACPs): Assembly with a 1,5-naphthylene bridged bis-bisurea ligand

A 1,5-naphthylene-bridged bis-bisurea receptor (L) has been designed and its coordination behavior with various anions has been examined in the solid state and in solution. This rigid "bis-bidentate" ligand can act as a linker to afford one-dimensional anion coordination polymers (ACPs) and dinuclear complexes with a wide range of anions. In the ACPs, the anions occupy the nodes and the polymeric structure is held solely by the coordination (hydrogen bonds) of the ligand to the anion. The sulfate ion forms three different complexes with L, two of which are discrete 1 : 2 (host-guest) anion complexes and the third is an ACP. The complexes of acetate and terephthalate are also 1D ACPs. On the other hand, benzoate, chloride and bromide ions form dinuclear complexes with L. Solution binding studies of L toward the anions were carried out by ¹H NMR, UV-vis and fluorescence titrations, from which the binding stoichiometry and stability constants were obtained.