Synthesis and co-ordination chemistry of a novel bis(benzo crown ether) substituted calix[4]arene that can simultaneously complex cations and anions

Abstract

New Calix[4]arene compounds substituted at the lower rim by four (L³) or two (L⁶) benzo-15-crown-5 (2,3,5,6,8,9,11,12-octahydro-1,4,7,10,13-benzopentaoxacyclopentadecine) groups respectively have been prepared. Proton NMR co-ordination studies with sodium and potassium cations in deuteriated acetonitrile revealed that L³ forms L³·5M⁺(M⁺= Na⁺ or K⁺) solution stoichiometric complexes consisting of an alkali-metal cation bound in each of the four crown ether moieties and one occupying the tetraamide lower-rim cavity. Compound L⁶ complexes K⁺, Ba²⁺ and NH₄⁺ exclusively at the crown ether binding sites in a 1:1 intramolecular sandwich stoichiometric fashion. A crystal-structure determination of [KL⁶][I₃] has been carried out. Although neither L³ nor L⁶ coordinates anions the potassium and ammonium complexes [ZL⁶]PF₆(Z = K⁺ or NH₄⁺) form 1:1 complexes with Cl^–, NO₃^–, HSO₄^– and H₂PO₄^–. Stability constant evaluations have shown that the strongest anion complexes are produced with H₂PO₄^– and HSO₄^–.