XPS Fe 2p peaks from iron tris(β-diketonates): Electronic effect of the β-diketonato ligand

Abstract

The Fe 2p photoelectron lines, as measured by X-ray photoelectron spectra (XPS), of a series of tris(β-diketonato)iron(III) complexes, are sensitive to the electron donating and withdrawing properties of the ligand attached to the iron atom. The maximum binding energy of the Fe 2p3/2 envelope revealed a linear relationship with the combined Gordy scale group electronegativity of the R-groups substituted on the respective β-diketonato ligand (RCOCHCOR′)−. A linear relationship between the binding energies and other electronic parameters was also obtained. Within these relationships, there are specific clusters of complexes defined by the amount of CF3 groups substituted per β-diketonato ligand. These specific clusters of complexes show an opposite trend inversely proportional to the general trend. It was also shown that the Fe 2p photoelectron peaks can be fitted with calculated multiplet splitting peaks, according to the synthetically generated multiplet splitting test spectra, as calculated by Gupta and Sen for a free Fe(III) ion. The tris(β-diketonato)iron(III) complexes containing unsymmetrically substituted β-diketonato ligands (RCOCHCOR′)−, were fitted with two different sets of multiplet splitting peaks, which are assigned to the fac and mer isomers of these complexes.