Transition metal 2p excitaton of organometallic compounds studied by electron energy loss spectroscopy

Oscillator strengths for Mn, Fe, and Co 2p excitation of dicyclopentadienyl, carbonyl and mixed ligand complexes have been derived from inner shell electron energy loss spectra (ISEELS) recorded under electric dipole scattering conditions. The spectra are found to be surprisingly sensitive to the identity of the ligands and/or the character of the metal-ligand bonding and apparently insensitive to the molecular symmetry or even the d count of the metal atoms. A simple model in terms of the relative energies of unoccupied orbitals of large 3d character involving in-line (“dσ*”) and off-axis (“dπ*”) interactions with ligand orbitals is proposed. Extended Huckel (EHT) calculations have been used to aid assignment of the observed spectral features. The EHT results suggest that the metal 2p spectra should be more sensitive to the molecular symmetry than is actually observed. The 2p spectra are compared to the metal 3p spectra of the same species and to the metal 2p spectra of the pure metals and various halide and oxide compounds.