The far-ultraviolet spectra of transition metal complexes

Abstract

The intense bands which are found beyond the d-d bands in the electronic absorption spectra of transition metal complexes are usually assigned to intra-ligand or charge transfer transitions. However, Rydberg transitions originating with either the mainly 3d or ligand orbitals are also expected to contribute in this part of the spectrum. To explore this the vapor phase electronic absorption spectra of the tri-hexafluoroacetyl-acetonate complexes of Al, Sc, V, Cr, Fe and Mn have been recorded up to about 80000 cm -1. In order to locate the Rydberg bands, quantum chemical calculations were carried out using the multiple scattering Xα MO method. Among the 4p and 4f type Rydberg bands there are several which are spin, Laporte, symmetry and angular momentum allowed and are expected to contribute strongly to the intensity observed in the ultraviolet and far-ultraviolet parts of the spectrum. The corresponding Rydberg states can mix, however, with valence-shell states of the same symmetry. The far-ultraviolet spectra of three sandwich compounds: bicyclopentadienyl Fe, Co and Ni were also determined. Due to the very low ionization potentials of these compunds, Rydberg transitions can contribute to the observed bands at rather low frequencies.