Cyclodextrin complexation of the tetracyanoquinodimethane anion radical: The chemical consequences of cavity size and alkyl derivatization

Jackie L. Beckett, Cynthia J Hartzell, Nathan L. Eastman, Theodore Blake, Michael P. Eastman

Research output: Contribution to journalArticle

9 Scopus citations

Abstract

Optical spectroscopy shows that in aqueous solution the tetracyanoquinodimethane anion radical (TCNQ-) exists in equilibrium with its π-π dimer (Boyd and Phillips). A study of the effect of various cyclodextrins on this equilibrium shows strikingly different results depending on cavity size and on alkyl derivatization. The equilibrium is unaffected by the presence of α-cyclodextrin. In contrast, γ-cyclodextrin complexes and stabilizes the π-π dimer. EPR and optical spectroscopy show that the anion radical is included and stabilized by heptakis(2,6-di-o-methyl)-β-cyclodextrin and a 2-hydroxypropyl derivative of β-cyclodextrin. Of great interest is the observation that the complex formed by TCNQ- and β-cyclodextrin rapidly reacts to form a diamagnetic product. Aqueous solutions of this diamagnetic product give evidence of appreciable concentrations of TCNQ- when heated or when low dielectric solvents like methanol are added. NMR indicates that the diamagnetic product is a dianion formed by the σ bonding of two β-cyclodextrin complexed anion radicals. σ-Bonded dimers of TCNQ- have been previously observed only in the solid phase (Vu Dong et al., Harms et al.). The tetrafluorotetracyanoquinodimethane anion radical exhibits the same general cyclodextrin chemistry as TCNQ-.

Original languageEnglish (US)
Pages (from-to)4173-4179
Number of pages7
JournalJournal of Organic Chemistry
Volume57
Issue number15
StatePublished - 1992

    Fingerprint

ASJC Scopus subject areas

  • Organic Chemistry

Cite this