Polarized absorption spectra of single crystals of ferrocene and its molecular complexes

Abstract

The polarized absorption spectra in the 9–40 rK region were observed on small single crystals of ferrocene, ferrocene-TCNE comples and ferricenium picrate by using a microspectrophotometer. It is shown that the 22.7 and 30.5 kK band systems of ferrocene cyrstal can be quantitatively explained on the basis of oriented-gas model. The solid molecular complex of ferrocene and TCNE is confirmed to be of charge-transfer type. The charge-transfer band is strongly polarized in the direction of [1 1 0] axis of crystal. It is concluded that the overlap between the π-electron orbital of cyclopentadienyl ring of ferrocene and that of TCNE is of primary importance in the charge-transfer interaction between ferrocene and TCNE molecules. The sharp absorption band of ferricenium ion located at 16 kK is shown to appear in the crystal spectrum of ferricenium picrate without appreciable change in the location of peak as well as in the band shape. No charge-transfer band can be found in the low-energy region of the spectrum of this crystal.