Correlation between Moessbauer isomer shifts and XPS binding energies

A series of low-spin pentacyanoferrates(II) of the type Na3[Fe(CN)5L] (L=phosphine or phosphite) have been characterized by 57Fe Moessbauer spectroscopy and X-ray photoelectron spectroscopy. The Fe-P bond in Na3[Fe(CN)5L] is discussed in terms of a correlation between the isomer shift and the binding energy. It has been demonstrated that the isomer shift increases with the decreasing Fe2p3/2 binding energy. The Moessbauer isomer shift reflects the total electron density at the nuclear site, while the chemical shift in the binding energy is concerned with the electron density on the atom of interest. The increasing Fe-to-P back donation leads to an increase of the s-electron density at the iron nucleus, i.e. a decrease of the isomer shift. The increasing tendency in the Fe2p3/2 binding energy is interpreted by the increasing Fe-to-P back donation. (orig.)