INNER-SHELL EXCITATION OF ETA-5-C5H5CO(CO)2 AND RELATED-COMPOUNDS STUDIED BY GAS-PHASE ELECTRON-ENERGY LOSS SPECTROSCOPY

Oscillator strengths for carbon 1s, oxygen 1s and cobalt 2p excitation of CpCo(CO)2 (Cp = eta-5-cyclopentadienyl) have been derived from inner-shell electron energy loss spectra recorded under scattering conditions dominated by electric dipole transitions. The spectral features have been assigned on the basis of comparison with the spectra of the free ligands and with previously studied gas phase organocobalt complexes, Co2 (CO)8 and Co (Cp)2, along with extended Huckel molecular orbital calculations. Comparisons of the core spectra of free and complexed ligands provide information on metal-ligand bonding. A simulation of the C1s spectrum of CPCO(CO)2, a weighted sum of the Co2 (CO)8 and Co (Cp)2 spectra, duplicates all features of the experimental spectrum, implying that the virtual orbitals of the ligands (as sampled by core excitation) are relatively independent of those of the other ligands. Quantitative deviations from this "building block" model reveal that the virtual MOs associated with Cp are more influenced by ligand-ligand interaction than those associated with the carbonyl ligand. These results provide a first view of the extent to which core excitation spectroscopy will be useful in studying the electronic structure of complex organometallic compounds with mixtures of ligands.