Correlation between Mössbauer isomer shifts and XPS binding energies

Abstract

A series of low-spin pentacyanoferrates (‖) of the type Na₃[Fe-(CN)₅L] (L = phosphine or phosphite) have been characterized by⁵⁷Fe Mössbauer 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 Fe2p_3/2 binding energy. The Mössbauer 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 Fe2p_3/7 binding energy is interpreted by the increasing Fe-to-P back donation.