An electrochemical and optical anion chemosensor based on tripodal tris(ferrocenylurea)

A neutral tripodal tris(ferrocenylurea) anion receptor has been designed that can electrochemically and optically recognize sulfate and phosphate anions. The binding of the tetrahedral anion induced distinct cathodic shifts of the ferrocene/ferrocenium redox couple in chloroform, whereas the UV/Vis spectrum of the receptor showed an increase in the d-d transition band upon addition of sulfate ions. Furthermore, the anion complexes (TBA)₂·[SO ₄⊂L]·H₂O (1) and TBA[F⊂L] (2; TBA=tetrabutylammonium ion) were isolated. Crystal structural analyses showed that the receptor in the two 1:1 (host/guest) complexes encapsulated sulfate or fluoride ions in the tripodal cavity through multiple hydrogen bonds. ¹HaNMR spectroscopic and ESI mass-spectrometric analysis revealed strong sulfate and fluoride binding in solution.