Electronic structure of cyanide and hexacyanoiron(II) anions using X-ray emission and X-ray photoelectron spectroscopies

Abstract

X-ray emission (X.e.) and X-ray photoelectron (X.p.) spectra have been recorded for sodium and potassium hexacyanoiron(II) and also for potassium cyanide. Core-orbital photoelectron data enables the X-ray emission spectra and the valence-band photoelectron spectrum to be aligned on a common energy scale. Peak coincidence in X.p. and X.e. spectra of the Fe^II complex identified the least tightly bound orbitals as predominately Fe 3d and showed that the group orbitals with the next highest ionisation energy had not only N 2p and C 2p(as in CN^–) character but also Fe 3d and Fe 4p character due to covalent ligand–iron bond formation. Relative peak intensities in the X.p., and absences in the X.e., spectra indicated that the main peak in the valence-band region was composed of 2s orbitals (presumably both C and N) but that the ligand molecular orbitals giving rise to this peak played little part in bonding to iron. Comparisons of molecular-orbital ionisation energies and atomic-orbital coefficients with theoretical calculations showed only qualitative greement.