title: Ion-Pair Complexation with Dibenzo[21]Crown-7 and Dibenzo[24]Crown-8 bis-Urea Receptors.
abstract: Synthesis and ion-pair complexation properties of novel ditopic bis-urea receptors based on dibenzo[21]crown-7 (R(1) ) and dibenzo[24]crown-8 (R(2) ) scaffolds have been studied in the solid state, solution, and gas phase. In a 4:1 CDCl3 /[D6 ]DMSO solution, both receptors clearly show positive heterotropic cooperativity toward halide anions when complexed with Rb(+) or Cs(+) , with the halide affinity increasing in order I(-) <Br(-) <Cl(-) . In solution, the rubidium complexes of both receptors have higher halide affinities compared to the caesium complexes. However, Rb(+) and Cs(+) complexes of R(2) show stronger affinities toward all the studied anions compared to the corresponding cationic complexes of R(1) . Similar selectivity of the receptors toward the studied ion pairs was also observed also in the gas phase by competition experiments with mass spectrometry. A total of eight crystal structures with different rubidium and caesium halides and oxyanions were obtained in addition to the crystal structure of R(2) ⋅BaCl2 . The selectivity observed in solution and in the gas phase is explainable by the conformational differences observed in the crystal structures of ion-pair complexes with R(1) and R(2) . In the solid state, R(1) has an open conformation due to the asymmetric crown-ether scaffold, whereas R(2) has a compact, folded conformation. Computational studies of the ion-pair complexes of R(2) show that the interaction energies of the complexes increase in the order CsI<CsBr<CsCl<RbCl, supporting the selectivity observed in solution and the gas-phase.
authors: University of Jyvaskyla, Department of Chemistry, Nanoscience Center, P.O. Box 35, 40014 University of Jyvaskyla, Finland.
authors: Toni
authors: T
authors: Mäkelä
authors: University of Jyvaskyla, Department of Chemistry, Nanoscience Center, P.O. Box 35, 40014 University of Jyvaskyla, Finland.
authors: Anniina
authors: A
authors: Kiesilä
authors: University of Jyvaskyla, Department of Chemistry, Nanoscience Center, P.O. Box 35, 40014 University of Jyvaskyla, Finland.
authors: Elina
authors: E
authors: Kalenius
authors: University of Jyvaskyla, Department of Chemistry, Nanoscience Center, P.O. Box 35, 40014 University of Jyvaskyla, Finland. kari.t.rissanen@jyu.fi.
authors: Kari
authors: http://orcid.org/0000-0002-7282-8419
authors: K
authors: Rissanen
keywords: crown compounds; ditopic receptors; hydrogen bonds; ion pairs; supramolecular chemistry