X-ray photoelectron spectroscopy study of a cyclic hexanuclear cluster

We report on a study of a ferric-wheel system by X-ray photoelectron spectroscopy. The sample investigated was a cyclic hexanuclear Fe(III) cluster entrapping an alkaline ion: [Li⊂Fe6L6]Cl, LN(CH2CH2O)3. The Fe 3s and 2p photoelectron spectra recorded for the ferric wheel and other Fe compounds, where Fe has the formal valence state 3+ or 2+, were compared. Uncommonly spectral features of the 3s line were qualitatively explained. It seems that unlike the usual transition metal compounds the electron energy configuration in the cluster favors the population of a final state with high-spin arrangement of electrons and a ligand hole. This could be due to covalency in such molecular compounds.