Anion recognition and sensing of ruthenium(ii) and cobalt(ii) sulfonamido complexes

Abstract

A series of artificial receptors, based on a sulfonamido system, have been designed and synthesized. The interaction of these receptors with biologically important anions was determined by UV-vis, ¹H NMR titration and electrochemical experiments. Results indicate that these receptors show high recognition abilities for fluoride (F⁻) or acetate (AcO⁻), moderate affinities for dihydrogen phosphate (H₂PO₄⁻) or hydroxyl (OH⁻) and almost no affinities for chloride (Cl⁻), bromide (Br⁻) or iodide (I⁻). ¹H NMR titration shows that the interaction between the receptors and anions depends on the hydrogen-bond formation. The Co^III/Co^II redox signals of receptor 3 and 4 disappear gradually when the fluoride or acetate anions are added. Moreover, visual color changes accompany guest binding, enabling this system to act as colorimetric anion sensors. The colorimetric properties of these sensors are ascribed to the hydrogen-bond formation and the colorimetric group quinoxaline.