Disposition of Ferrocenes in β- or γ-Cyclodextrin Cavity and Consideration on the Absorption Bands of Ferrocene

Abstract

By comparing the induced circular dichroism (ICD) spectrum of 1,4,7,10,13-pentaoxa[13](1,1′)- ferrocenophane, I, in the presence of β-cyclodextrin (β-CDx) with that of ferrocenes (Fcs) in β-CDx or γ-CDx cavity, the disposition of Fcs in the CDxs is determined. Thus, the orientation of Fc in the Fc: β-CDx 1:1 complex and ferrocenecarboxylic acid (FcMA) in β-CDx at pH 2 is considered to be nearly parallel to the molecular axis of β-CDx, while that of Fc in the Fc: γ-CDx 1 : 1 complex, FcMA in β-CDx cavity at pH 9, and FcMA and ferrocenedicarboxylic acid (FcDA) in γ-CDx cavity appears to be close to normal to the molecular axis of the CDx. In addition, based on the ICD spectra, an intense band of Fcs at around 200 nm is assigned as a charge–transfer (CT) transition between the cyclopentadienyl (Cp) rings and iron(II). The advantage of using CDxs for the determination of the polarization direction of absorption bands of chromophore molecules is mentioned in comparison with previous methods.