Moessbauer spectroscopic study of oxo-centered mixed-valence trinuclear iron fumarate

Oxo-centered mixed-valence trinuclear iron dicarboxylic acid complex iron fumarate [Fe3O(O2CCH=CHCO2)3(H2O)3] x nH2O (n = 18∼19), have been synthesized firstly. Variable temperature Moessbauer spectroscopy has been carried out to elucidate the rate of intramolecular electron transfer. It was found that the complex showed a temperature dependent mixed-valence state. At low temperature two quadrupole split doublets were observed corresponding to high spin Fe(III) and high spin Fe(II) state and a complete averaged valence state was observed at about 270 K. At temperatures between 200 and 270 K the spectra showed relaxation effect as the electron transfer rate was comparable to the Moessbauer timescale (∼10-7 s). (author)