Use of X-Ray Photoelectron Spectroscopy to Study Bonding in Cr, Mn, Fe, and Co Compounds

The photoelectron spectra of some 40 transition metal compounds have been measured using AlKα(1487 eV) and MgKα(1254 eV) x-rays. The compounds included both simple salts (halides and chalcogenides) and hexacoordinated complexes (cyano- and fluoro-) of Cr(III), Mn(II, III), Fe(II, III), and Co(III). From these data we have determined the chemical shifts of the core electrons and related these results to a calculated charge based on Pauling's electronegativities. In addition, multiplet splitting has been obtained for photoionization in the 3s shell and is discussed in terms of the exchange interaction between the partially filled 3s and 3d orbitals. To help in this explanation, calculations were made using both (1) Hartree-Fock solutions of the wavefunctions for free ions and (2) a qualitative evaluation of the behavior of the exchange integral. The value of using x-ray photoelectron spectroscopy for studying chemical bonding for transition metal compounds is amply illustrated.