Unusual charge distributions in some bis(fulvalene)dimetal complexes as revealed by x-ray photoelectron spectroscopy

A series of bis(fulvalene)dimetal species, ((C/sub 10/H/sub 8/)/sub 2/M/sub 2/)/sup n+/, was studied by using X-ray photoelectron spectroscopy. Some of the complexes have metal binding energies which are lower than one would expect, assuming the ligands to be dianions. These data are rationalized by considering the metal atoms to be in reduced oxidation states and the fulvalene ligands to be partially oxidized. The metal 2p spectra of the mixed-valence compounds (n=1) of cobalt and nickel show line broadening indicative of two inequivalent core-ionized states. Most of the paramagnetic compounds show an increase in spin-orbit splitting and line broadening attributable to multiplet splitting. Satellite structure, arising from ligand-to-metal charge-transfer transitions, appears in the spectra of some of the paramagnetic compounds.