Complexation between methyl viologen (paraquat) bis(hexafluorophosphate) and dibenzo[24]crown-8 revisited

Travis B. Gasa, Jason M. Spruell, William R. Dichtel, Thomas J. Sørensen, Douglas Philp, J. Fraser Stoddart, Petr Kuzmič

Research output: Contribution to journalArticlepeer-review

55 Scopus citations

Abstract

Paraquat bis(hexafluorophosphate) undergoes stepwise dissociation in acetone. All three species - the neutral molecule, and the mono- and dications - are represented significantly under the experimental conditions typically used in host-guest binding studies. Paraquat forms at least four host-guest complexes with dibenzo[24]crown-8. They are characterized by both 1:1 and 1:2 stoichiometries, and an overall charge of either zero (neutral molecule) or one (monocation). The monocationic 1:1 host-guest complex is the most abundant species under typical (0.5-20 mM) experimental conditions. The presence of the dicationic 1:1 host-guest complex cannot be excluded on the basis of our experimental data, but neither is it unambiguously confirmed to be present. The two confirmed forms of paraquat that do undergo complexation - the neutral molecule and the monocation - exhibit approximately identical binding affinities toward dibenzo[24]crown-8. Thus, the relative abundance of neutral, singly, and doubly charged pseudorotaxanes is identical to the relative abundance of neutral, singly, and doubly charged paraquat unbound with respect to the crown ether in acetone. In the specific case of paraquat/dibenzo[24]crown-8, ion-pairing does not contribute to host-guest complex formation, as has been suggested previously in the literature.

Original languageEnglish (US)
Pages (from-to)106-116
Number of pages11
JournalChemistry - A European Journal
Volume15
Issue number1
DOIs
StatePublished - 2009

Keywords

  • Crown compounds
  • Donor-acceptor systems
  • Ion pairs
  • Paraquat
  • Supramolecular chemistry

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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