Alkali metal cation cooperative anion recognition by heteroditopic bis(calix[4]arene) rhenium(I) bipyridyl and ferrocene receptor molecules

Abstract

New heteroditopic bis(calix[4]arene) rhenium(I) bipyridyl (L¹, L²) and ferrocene (L⁴) receptor molecules have been prepared and shown to bind a variety of anions at the upper rim and alkali metal cations at the lower rim. Proton NMR anion titration studies reveal the strength and selectivity of anion binding was dependent upon the presence of the calix[4]arene moieties and nature of the bridging group with the preorganised receptors L¹ and L² forming strong complexes in deuterated DMSO solutions. With L¹, L² and L⁴ co-bound lithium, sodium and potassium cations were found to significantly enhance the strength of iodide binding in acetonitrile solutions with the largest positive cooperative binding effect observed with L² and sodium cations. Cyclic voltammetric investigations revealed L⁴ to electrochemically recognise carboxylate and halide anions. In the presence of lithium cations the electrochemical response of L⁴ to bromide anions was significantly amplified.