ELECTRONIC SPECTRA OF HEXAHALOGENO COMPLEXES OF OSMIUM(IV), RHENIUM(IV) AND PLATINUM(IV)

Kozikowski, Barbara Ann

Abstract

Electronic d-d transitions within the t_2g⁴ configuration of Os⁺⁴ doped into cubic crystals of Cs₂ZrCl₆ and Cs₂ZrBr₆ were studied by means of low temperature absorption and magnetic circular dichroism (MCD) spectroscopy. The observed spectra are dominated by sharp vibronic features at liquid helium temperatures; an analysis of the vibronic and MCD spectra allowed the identification of all six excited states of the t_2g⁴ manifold in both hexahalogeno systems. The observed energy levels are compared to the results of complete ligand field calculations in the weak field basis set.

An analysis of the low temperature absorption spectra of Os⁺⁴ doped into K₂SnCl₆, and pure crystals of K₂OsCl₆ and K₂OsBr₆, is also presented. The experimentally determined energy levels in these various crystalline hosts are all mutually consistent.

An analysis of the low temperature absorption and MCD spectra of Re⁺⁴ in Cs₂ZrCl₆ and Cs₂ZrBr₆, and the absorption spectra of Re⁺⁴ in K₂SnCl₆, allowed the identification of all five excited states of the t₂g³ configuration; the resultant energy levels are compared to the results of complete ligand field calculations.

The ligand field model proved to be inadequate in completely describing the energy levels in these heavy transition metal systems. In particular, the energy levels are only marginally dependent on the crystal field parameter D_q; therefore, this parameter could not be reliably determined. Reasonable estimates on the magnitude of the remaining ligand field parameters were made on the basis of optimized ligand field calculations for both Os⁺⁴ and Re⁺⁴ systems.

An analysis of the two-photon excitation spectra of a single crystal of K₂PtCl₆ is also presented. Data is reported at 2K and 77K using laser excitation in the range of 680 to 950 nm. This is the first measurement of a two-photon d-d transition in a transition metal complex.