HE(I) PHOTOELECTRON-SPECTRA OF PENTACARBONYL(SELENOCARBONYL)CHROMIUM(O) AND RELATED COMPLEXES

The He(I) p.e. spectrum of Cr(CO)5(CSe) has been measured and all the ionization potentials are slightly lower than those reported earlier for the related thiocarbonyl derivative. The bands associated with the σ-donor and π-acceptor levels of the CSe ligand are well sepa rated from the other bands and appear in the 10-11.5 eV range, i.e., in between the bands for the metal 3d and the carbonyl ligands. The decrease in binding energies on replacement of a CO group in Cr(CO)6 by CSe is at variance with the known physical and chemical properties of this and other selenocarbonyl complexes and is most probably due to a destabilization of the metal orbitals similar to that suggested for metal thiocarbonyl complexes The first ionization potentials of BzCr(CO)2(CX) (Bz = η6-C6H6; X = O, S, Se) were also measured and comparison of these values with those for the corresponding Cr(CO)5(CX) species indicates that there is a significant transfer of electron density from the benzene ring to the chromium atom in each case. © 1979.