When compared to crown ethers
and cryptants, calixarenes carry metal cations from one phase to the other more selectively.
In earlier studies the extractant properties of some crown ether macrocycles carrying oxygen nitrogen and sulfur donors has been investigated and the results disclosed selective crown ethers for some transition metal cations such as Ag+ and Hg2+.
It is well known that the extractability of metal ions with macrocylic reagents such as crown ether and cryptand is governed by the stability of the metal complexes .
In these studies we generally found that dichloromethane is more effective solvent than chloroform in the extraction of transition metal cations with macrocyclic crown ether carrying nitrogen-oxygen-sulfur mixed donor atoms.
Synergistic solvent extraction and separation of lanthanoids with mixtures of 1-phenyl -3-methyl -4-benzoyl-5-pyrazolone and crown ethers.
Crown ethers as synergistic agents in the solvent extraction of trivalent lanthanoids with thenoyltrifluoroacetone.
Different crown ethers have different binding capacity with the same cation, owing to the size of the cavity.
The dicylcohexano crown has the highest complexation constant of the crown ethers, and this appears to be completely intercalated.
Crown ethers act almost exclusively on positively charged ions, readily unfolding and stretching to engulf their unwitting guests.
Cram and his group have concentrated on building rigid molecules that, unlike crown ethers, have a permanent cavity.
MeasurementsBuschmann's methodA spectrophotometric method to determinethe complex stability constants of the ammonium and alkylammonium ions with many of dibenzo crown ethers in aqueous solution was developed by K= [LM ] [L] [Mn+] (2) Buschmann .
The correctness of these assumptions has already been showed for some macrocyclic ligands such as benzo and aza crown ethers cryptands and cucurbit[n]urils [19-23].