Binding and Detection of Anions Using Tripodal Hosts

Abstract

The aim of this project was to investigate the anion-binding properties of a range of different receptor compounds. For the most part, the receptors reported here were tripodal in nature, wherein three hydrogen-bonding receptor groups, including amines, amides and ureas, are linked around a common structural core. In this study, a range of different cores were chosen, such as simple and flexible organic frameworks based on the tris(2-aminoethyl)amine (tren) precursor, conformationally-restricted and brightly coloured aromatic species based on the dye pararosaniline, and triply-ligated metal complexes of ruthenium(II).
In order to assess the anion binding abilities of these receptors, a range of different techniques were employed, with 1H-NMR and UV/Visible spectroscopic titrations being the most common. Additionally, the incorporation of fluorescent pyrene moieties as a reporter group to some of the receptors allowed for the probing of anion binding via fluorimetric titrations in these cases.
During the course of the experiments, a number of interesting, and in some cases, unexpected, binding conformations were found – in particular, the interactions between many of the organic receptor compounds with the planar 1,3,5-benzenetricarboxylate (trimesylate) trianion, and the pH dependency of the colour of the pararosaniline-based receptors. Additionally, the range of cyclic thioether-capped ruthenium(II) receptor compounds reported here showed an unusually high resistance to degradation by solvent and guest when compared to similar receptors with aromatic-capped ruthenium, and successfully gave tripodal ML3 complexes instead of the traditionally more stable ML2X dipodal complexes.