Macrocyclic ligands polyethers

Another group of macrocyclic ligands that have been extensively studied are the cycHc polyethers, such as dibenzo-[18]-crown-6 (5), in which the donor atoms are ether oxygen functions separated by two or three carbon atoms. The name crown ethers has been proposed (2) for this class of compounds because of the resemblance of their molecular models to a crown. Sandwich stmctures are also known in which the metal atom is coordinated with the oxygen atoms of two crown molecules. 

A polymeric stack of macrocycles has been synthesized [6.72] and a cyclodextrin-based model of a half-channel has been reported [6.73]. Channel-type conduction of Na+ ions has been reported for a tris-macrocyclic ligand [6.74]. A derivative of the acyclic polyether ionophore monensin forms lithium channels in vesicles [6.75a], which may be sealed by diammonium salts [6.75b]. 

Macrocyclic ligands. Cations of the group one metals form stable complexes with macrocyclic polyethers, for example, Na and 18-crown-6, ( 0-CH2-CH2-)6. 

Pedersen s discovery of macrocyclic polyethers (crown ethers) represents one of the most significant innovations in organic chemistry in recent years specific complexation of the cation by the macrocyclic ligand both facilitates the solubility... 

The use of interlocked polyether-diimine macrocycle ligand (Fig. 5) has interesting implications for the coordination of metal ions, especially those of iron [32]. 

Poly (macrocyclic) compounds. The analytical application of compounds such as crown polyethers and cryptands is based on their ability to function as ligands and form stable stoichiometric complexes with certain cations. Special importance is due to their preference for alkali metal ions which do not form complexes with many other ligands. A number of these compounds are commercially available and their properties and analytical applications have been described by Cheng et a/.11... 

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