X-ray photoelectron spectroscopy and multiple scattering Xa calculations have been applied to a series of iridium halide complexes in order to corroborate the nature of the bondings inherent in this class of compounds. Our results seem to substantiate contentiously that higher oxidation states of indium favor the formation of covalent bonds. This conclusion is based on the observation that (1) successive bombardment of the iridium species by Ar ions almost definitely leads to a configuration in which indium is bound to at most one halide ion, and (2) the theoretical charge per ligand ion approaches systematically a value of {I -} in the limit as the formal oxidation state of indium approaches {l+}. The theoretical results are further authenticated by the fact that the experimental ionization energy of the Ir(4f) level in the different iridium halide complexes studied is seen to decrease as a result of exposure to Ar ions.

The relativistic multiple scattering Xα method has been applied in order to calculate the eigenvalues and the charge densities of cis and trans diaminodichloroplatinum(II). The activity of the cis isomer as an antitumor agent is discussed in terms of the possible modes of coordination of certain fragments of the DNA molecule through the LUMO state of the cis Pt complex. Although possible, coordination of the trans isomer is rendered unlikely as a result of possible strain effects.

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006ChemInform Abstract MS-Xα calculations, applied to a series of hexaiodoiridate complexes in order to study important charge-transfer processes, predict iridium(IV) complexes to exhibit more covalent character than iridium complexes with lower oxidation states. This trend s confirmed by experimental photoelectron results.

A new technique for the study of charge transfer processes is presented. The method is based on electron density differentials and employs multiple scattering Xa molecular wave functions. The method is discussed with reference to an excitation of an electron from the HOMO to the LUMO of bis(g1ycinohydroxo-mato) nickel (11).