A new class of redox-active ionophore comprised of two calix[4]diquinone moieties connected through either alkylene or pyridylene linkages has been developed. Spectroscopic and electrochemical investigations, X-ray crystal structure analyses, and molecular modeling studies show butylene- and propylene-linked members of this family of redox-active receptors exhibit remarkable selectivity preferences and substantial electrochemical recognition effects toward cesium and rubidium cations.
A ditopic receptor comprised of a calix [4]semitube for cation recognition and urea functionality for anion complexation has been developed. This receptor displays a remarkable selectivity and fast kinetics of complexation for potassium cation over all other Group 1 metal cations, a property mirroring that of the parent calix[4]semitube 1. 1 H NMR studies reveal that 4 cooperatively binds a range of sodium and potassium halide and acetate salts in 2 : 1 CDCl 3 : CD 3 CN, with anion binding enhancements of over thirty-fold in the case of bromide. Extraction experiments demonstrated that the host could solubilise sodium and potassium salts in chloroform.
H NMR binding studiesGroup 1 metal cation complexation. Preliminary experiments were undertaken on the ditopic calix[4]semitube 4 to establish the receptor's kinetic complexation behaviour towards Na ϩ , K ϩ and Rb ϩ cations. The addition of one equivalent of NaClO 4 , KPF 6 or RbPF 6 to 5 : 1 CDCl 3 : CD 3 CN and 4 : 1 CDCl 3 : CD 3 OD solutions of 4 revealed that although the complexation/decomplexation process was slow on the NMR timescale, Scheme 1 Synthesis of the heteroditopic receptor.
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