Spectrophotometric Study of Complexation of Dicyclohexano-24-crown-8 with [60]- and [70]Fullerenes and Other Acceptors

Abstract

Molecular complex formation of dicyclohexano-24-crown-8 with electron acceptors such as [60]- and [70]fullerenes, menadione (vitamin K3), and o- and p-chloranils have been studied in CCl4 medium. Charge trasfer (CT) absorption bands have been obtained in four cases which correlate well with the electron affinities of the acceptors. In the case of the [70]fullerene complex, an isosbestic point has been obtained. Entropies and enthalpies of formation of the [60]- and [70]fullerene complexes with the crown ether have been determined by estimating the formation constants spectrophotometrically at five different temperatures. It is observed that the crown ether under consideration does not form inclusion complexes with the fullerenes although the corresponding crown ether with a benzene ring instead of cyclohexane ring is known to include [60]fullerene in preference to [70]fullerene. The conformational flexibility of the cyclohexane ring affects the cavity size of the crown and thus hinders inclusion complex formation.