Ion Receptors

Ion receptors could be used for the extraction of toxic or radioactive cations and anions from water or the recycling of valuable raw materials, providing means for water purification and decontamination. Supramolecular chemistry has been concerned with cation receptors since the seminal work of Pedersen, Lehn, and Cram on crown ethers, cryptands, and spherands, respectively. Since then, cation receptor chemistry represents an important research field, which has also addressed the challenge of developing systems that can efficiently work in water. Cations are classified into three categories: electropositive inorganic cations, transition metal ions, and organic cations. To illustrate the strategies available for the development of anion receptors, this chapter presents representative examples for different receptor classes. Most examples focus on receptors for inorganic anions or carboxylates. Zwitterion receptors contain two complementary binding sites, one for the cationic and one for the anionic part of the substrate.