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Calix[4]pyrrole‐Based Heteroditopic Ion‐Pair Receptor That Displays Anion‐Modulated, Cation‐Binding Behavior
Author(s) -
Park InWon,
Yoo Jaeduk,
Adhikari Suman,
Park Jung Su,
Sessler Jonathan L.,
Lee ChangHee
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201202777
Subject(s) - chemistry , ion , fluoride , halide , perchlorate , pyrrole , salt (chemistry) , chloride , inorganic chemistry , crystallography , medicinal chemistry , stereochemistry , organic chemistry
A new ditopic ion‐pair receptor 1 was designed, synthesized, and characterized. Detailed binding studies served to confirm that this receptor binds fluoride and chloride ions (studied as their tetraalkylammonium salts) and forms stable 1:1 complexes in CDCl 3 . Treatment of the halide‐ion complexes of 1 with Group I and II metal ions (Li + , Na + , K + , Cs + , Mg 2+ , and Ca 2+ ; studied as their perchlorate salts in CD 3 CN) revealed unique interactions that were found to depend on both the choice of the added cation and the precomplexed anion. In the case of the fluoride complex [ 1⋅ F] − (preformed as the tetrabutylammonium (TBA + ) complex), little evidence of interaction with the K + ion was seen. In contrast, when this same complex (i.e., [ 1⋅ F] − as the TBA + salt) was treated with the Li + or Na + ions, complete decomplexation of the receptor‐bound fluoride ion was observed. In sharp contrast to what was seen with Li + , Na + , and K + , treating complex [ 1⋅ F] − with the Cs + ion gave rise to a stable, receptor‐bound ion‐pair complex [Cs ⋅1⋅ F] that contains the Cs + ion complexed within the cup‐like cavity of the calix[4]pyrrole, which in turn was stabilized in its cone conformation. Different complexation behavior was observed in the case of the chloride complex [ 1⋅ Cl] − . In this case, no appreciable interaction was observed with Na + or K + . In addition, treating [ 1⋅ Cl] − with Li + produces a tightly hydrated dimeric ion‐pair complex [ 1⋅ LiCl(H 2 O)] 2 in which two Li + ions are bound to the crown moiety of the two receptors. In analogy to what was seen in the case of [ 1⋅ F] − , exposure of [ 1⋅ Cl] − to the Cs + ion gives rise to an ion‐pair complex [Cs ⋅1⋅ Cl] in which the cation is bound within the cup of the calix[4]pyrrole. Different complexation modes were also observed when the binding of the fluoride ion was studied by using the tetramethylammonium and tetraethylammonium salts.