Crown Ethers

Model Compounds for Size Selection of Singly Charged Cations


For transport in biological systems, alkali ions are bound by special ligands, called ionophores. These ligands show remarkable ion selectivity, which is usually determined by the size of the corresponding cations.


Similar selectivity can be observed by crown ether complexes, which selectively bind different alkali metal ions depending on the ring size.


Hole diameter: 120-150 pm

Hole diameter: 170-220 pm

Hole diameter: 260-320 pm

Hole diameter: 340-430 pm

Li+-Ion: Ø 152 pm
Na+-Ion: Ø 204 pm
K+-Ion: Ø 276 pm
Rb+-Ion: Ø 304 pm

Click on the pictures of the ions to see the structures of the complexes.