Calixarenes anion complexation

The performance of calixarenes as cation carriers through H20-organic solvent H20 liquid membranes has also been studied.137 In basic metal hydroxide solutions, the monodeprotonated phenolate anions complex and transport the cations, while [18]crown-6 does not, under the same conditions. Low water solubility, neutral complex formation and potential coupling of cation transport to reverse proton flux have been cited as desirable transport features inherent in these molecules.137... 

The calixarene-M3+ complex is formed at the interface and remains there due to its surface activity neutralization by cosan anions removes the amphiphilic character and allows diffusion into the bulk organic phase... 

P-5 A phosphinic calixarene is complexed to four Ag(I)Q molecules and one additional chloride ion to give an anion (161) that can act as host for alkali metal cations, Hg(II) and Pb(II)235 236. 

Figure 13 illustrates all the known modes of cation binding by native and functionalized calixarenes exploiting cation-TT, induced dipole, or electrostatic interactions. Strictly speaking, only for situations (c)-(f), we can talk of cation recognition by calixarene receptors, whereas in metallation with transition and f-element (situations (a) and (b)), which are often exploited in anion complexation or catalysis, little control is experienced on selectivity. Usually, the most important calixarene-based cation receptors are obtained by the introduction of chelating units at the lower rather than at the upper rim. This ensures a more... 

The increase in stability constant can be ascribed to (i) an increase in acidity of the urea NH protons because of the electron withdrawing effect of the bound cation (ii) the rigidification of the calixarene units by cation complexation and (iii) an electrostatic attraction between the bound cation and anion. Thus, this receptor cooperatively binds a range of sodium and potassium halides with the bound group 1 metal cation effectively switching on anion complexation. Extraction experiments demonstrated that the host is capable of solubilizing sodium and potassium salts in chloroform. 

Stepwise conversion of an olefin into an alkylidene has been reported in [calixarene]W(olefin) complexes. Where the olefin was ethylene or propylene, deprotonation afforded an anionic alkylidyne species, which on protonation... 

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