Chromogenic ligands for lithium based on calix[4]arene tetraesters bearing nitrophenol residues

Abstract

Three novel chromogenic calix[4]arene tetraesters bearing nitrophenol residues which dramatically change their UV–VIS absorbance spectra upon complexation with metal ions have been investigated. Upon addition of metal perchlorates such as lithium or sodium to a solution of the calixarene in tetrahydrofuran, in the presence of a base, a colour change from near colourless to yellow occurs. The colour density is dependent on metal perchlorate concentration and can be monitored by UV–VIS spectroscopy. All three compounds were found to be lithium selective with a 10–40 fold selectivity for lithium against sodium. No colour change was noted in the absence of a base. From two-phase studies, it has been demonstrated that all three ligands have the ability to extract metal ions from an aqueous phase into an immiscible organic phase (butan-1-ol) which had been made basic by the addition of the lipophilic base tridodecylamine, with a colour change from near colourless to yellow occurring in the organic phase. The deprotonated calixarene metal ion complex was found to diffuse into the aqueous phase with time, with the rate of diffusion being strongly dependent on the lipophilic nature of the calixarene backbone.