Oligoether‐Strapped Calix[4]pyrrole: An Ion‐Pair Receptor Displaying Cation‐Dependent Chloride Anion Transport

Abstract A ditopic ion‐pair receptor ( 1 ), which has tunable cation‐ and anion‐binding sites, has been synthesized and characterized. Spectroscopic analyses provide support for the conclusion that receptor 1 binds fluoride and chloride anions strongly and forms stable 1:1 complexes ([ 1⋅ F] − and [ 1⋅ Cl] − ) with appropriately chosen salts of these anions in acetonitrile. When the anion complexes of 1 were treated with alkali metal ions (Li + , Na + , K + , Cs + , as their perchlorate salts), ion‐dependent interactions were observed that were found to depend on both the choice of added cation and the initially complexed anion. In the case of [ 1⋅ F] − , no appreciable interaction with the K + ion was seen. On the other hand, when this complex was treated with Li + or Na + ions, decomplexation of the bound fluoride anion was observed. In contrast to what was seen with Li + , Na + , K + , treating [ 1⋅F ] − with Cs + ions gave rise to a stable, host‐separated ion‐pair complex, [F ⋅1⋅ Cs], which contains the Cs + ion bound in the cup‐like portion of the calix[4]pyrrole. Different complexation behavior was seen in the case of the chloride complex, [ 1⋅ Cl] − . Here, no appreciable interaction was observed with Na + or K + . In contrast, treating with Li + produces a tight ion‐pair complex, [ 1⋅ Li ⋅ Cl], in which the cation is bound to the crown moiety. In analogy to what was seen for [ 1⋅ F] − , treatment of [ 1⋅ Cl] − with Cs + ions gives rise to a host‐separated ion‐pair complex, [Cl ⋅1⋅ Cs], in which the cation is bound to the cup of the calix[4]pyrrole. As inferred from liposomal model membrane transport studies, system 1 can act as an effective carrier for several chloride anion salts of Group 1 cations, operating through both symport (chloride+cation co‐transport) and antiport (nitrate‐for‐chloride exchange) mechanisms. This transport behavior stands in contrast to what is seen for simple octamethylcalix[4]pyrrole, which acts as an effective carrier for cesium chloride but does not operates through a nitrate‐for‐chloride anion exchange mechanism.