Bonding studies from charge-transfer absorption and magnetic circular dichroism spectra. Part 3.—Meridional complexes of osmium(III)

Abstract

We have examined the m.c.d. and absorption spectra of a number of meridional complexes of Os^III and Ru^III of the general form MCl₃L₃. The spectra consist mainly of charge transfer transitions from filled ligand orbitals into the vacancy in the t_2g shell thus revealing the ordering of the filled bonding orbitals. We have used e.s.r. data to obtain quantitative information on the ground state and the Faraday parameters. This has led to an identification of the transitions observed below ∼40 000 cm^–1. As in Part 1 and Part 2 of this series we find that for L = PR₃ or AsR₃, charge transfer is a relatively low energy process which moves to higher energy for L = SR₂ or pyridine. One striking feature is the reduction of the energy of transitions to a mixed chloride, L σ-state which indicates a destabilisation of a Cl-metal σ bond. This appears to be a feature of the low symmetry of these complexes (C_2v) in which mixing may take place.