Electron Spin Resonance Studies on Gamma-Irradiated Ferrocene

Abstract

The aim of this study was to determine the nature of the free radicals induced in ferrocene by ⁶⁰Co gamma rays. The irradiations were carried out on the powder at 77°K, the temperature at which crystals have burst into powder form, and on the single crystals at 193°K. At 77°K two radicals are formed, I and II; I transforms itself into a third radical, III, on annealing at temperatures above 145°K. In the single crystals irradiated at 193°K, only radicals II and III are formed. When the single crystals were not too damaged, the disappearance of the radical III with concommitant appearance of a fourth radical, IV, which presents a hyperfine structure of five lines was observed. Taking into account the anisotropies of the $g$ tensors, change in spectra upon deuterium substitution of the cyclopentadienyl protons, and behavior on annealing, the spectra of radicals I–IV were attributed tentatively as follows: I to a straight molecule‐ferricinium ion, II to a protonated ferrocene radical, III to a bent molecule‐ferricinium ion, IV to a C₅H₅–Fe–C₅H₄·radical. Mechanisms are given for the formation of these radicals as well as for their disappearance on annealing.