Crown Ethers and Cryptands

Crown ethers have a strong affinity for specific cations, enabling them to act as phase-transfer catalysts. This property makes them particularly useful in facilitating reactions such as enolate formation and nucleophilic substitution by transferring ionic species into organic solvents. Crown ethers are named in the format m-crown-n, where m represents the total number of atoms in the ring, and n indicates the number of oxygen atoms in the ring that coordinate with cations.

Cryptands

Cryptands are a class of synthetic, cage-like molecules designed to bind cations, anions, or neutral molecules with exceptional selectivity and strength. Unlike crown ethers, which form two-dimensional rings, cryptands create a three-dimensional structure with multiple binding sites, offering a tighter and more specific fit. Their unique ability to encapsulate ions within their cavity makes them highly effective in phase-transfer catalysis and ion-selective processes. Cryptands are often named using the notation [m.n.p], where m, n, and p denote the number of binding atoms in each of the three linking chains that form the cage.

Cryptands form complexes with many "hard cations" including NH₄⁺, alkali metals, and alkaline earth metals.

[2.2.2]Cryptand

here

here

here