Interpretation of Electron Transfer Spectra of Iridium (IV) and Osmium(IV) Mixed Chloro-Bromo Complexes

Abstract

The previous M.O. treatment of unsubstituted hexahalides has been modified, taking the results on Faraday effect obtained at the University of Virginia into account. The absorption spectra previously measured of the complexes (M=Os, Ir) trans-MCl₄Br₂ ^— and trans-MCl₂ Br₄ ^— are interpreted by a M.O. treatment for the symmetry D_4h as electron transfer transitions, including a first-order relativistic (spin-orbit coupling) correction. The concept of holohedrized symmetry is sufficiently valid to allow a description of MCl₅Br^— and MClBr₅ ^— as if they were tetragonal with centre of inversion and ƒac-(or cis-)MCl₃Br₃ ^— as if they were cubic. It is shown that the ligand-ligand antibonding effects have the same order of magnitude as the moderate difference in optical electronegativity between Cl^- and Br^-.