Ionic recognition by thiacalixarenes: binding of alkali and heavy metal ions by thiacalix[4]arene-bis-crown[n] ethers

The binding properties of two thiacalix4]arene-bis-crownn] derivatives (n = 5 and 6) were examined through extraction experiments. The stability constants of the resulting complexes in methanol were determined. The replacement of the bridging CH2 groups by sulfur atoms leads to a strong decrease in both extraction and complexation levels of alkali metal ions but does not affect the selectivity within the series of crown ethers. The stability of complexes with heavy metal ions does not change markedly on passing from thiacalix4]arene-bis-crownn] ethers to their calix4]arene-bis-crownn] counterparts; therefore no clear-cut conclusions about the possible interactions between these cations and the sulfur atoms can be drawn.