The vibronic structure of mixed-ligand osmium(iv) complexes

Abstract

Mixed-ligand osmium(iv) complexes, OsCl5X2- and cis-OsCl4X2- 2, with X = Br or I, are optically investigated by recording the 10 K absorption spectra of the caesium and tetrabutylammonium salts in KBr pellets and the 10–20 K emission spectra of complexes doped in Cs2SnCl6, both in the energy region between 5000 and 17 000 cm-1. The measured peaks (origins and vibronics) are due to zero-phonon and vibronic transitions respectively within the (t2g)4 subshell configuration, which gives rise to a maximum of 15 energy levels at low symmetry. From the well-resolved absorption and emission spectra the d-level energies can be obtained for many of the split states that are expected in the region considered. For an assignment to symmetry types, selection rules for electric dipole transitions are applied, comparing peak intensities in the spectra. Ligand-field calculations using angular overlap parameters support these assignments, which must, however, be considered as partially tentative.