Anion Complexation by Meso-Octamethylcalix[4]pyrrole in Aqueous Solution

Abstract

The ligand calix[4]pyrrole is quite insoluble in aqueous solution. In the presence of NaCl, KCl, CsCl, NH₄Cl, CaCl₂, and CdCl₂, the solubility of calix[4]pyrrole linearly increases with the salt concentration. The ligand calix[4]pyrrole forms stable complexes with the chloride anion. All other halogen anions do not form complexes. The measurement of the amount of dissolved ligand allows the determination of the complex stabilities in aqueous solution. This experimental method is discussed in detail due to its general suitability to study the complexation reactions with nearly insoluble ligands.

Keywords:

• Anions
• Aqueous solution
• Complex formation
• Meso-octamethylcalix[4]pyrrole
• Solubility
• Stability

Acknowledgments

The authors are grateful to the NATO Scientific and Environmental Affairs Division for financial support under the Collaborative Linkage Grant No LST. CLG 979790.

Additional financial support by the Ministerium für Wissenschaft und Forschung des Landes Nordrhein-Westfalen is gratefully acknowledged.

Notes

^a Solubility in the presence of salt decreases, see Fig. 2.