A ligand field theory analysis of the spectra of thet2g3levels of IrF6

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Abstract
Calculations and experimental data are presented for the t 2g 3 molecular levels of IrF6 which imply that a substantial interaction takes place between these 5d3-configuration states and charge transfer states at ca. 20 000 cm-1. This t 2g 3-charge transfer state configuration interaction is so extensive that the five t 2g 3 levels can only be fit with physically unreasonable values of the Racah (electrostatic) parameters and a spin orbit coupling parameter that is not consistent with expectations for 5d-series transition metal hexafluorides. Parameter values presented for IrF6 are thus determined from the lowest three levels only, as these should experience the smallest relative shift due to configuration interaction: B = 297 cm-1, C = 1167 cm-1, ζ5d = 4182 cm-1, and 10Dq = 35 000 cm-1. In order to corroborate the assertion that t 2g 3-charge transfer configuration interaction is an important factor for the determination of IrF6 crystal and molecular properties, a number of t 2g 3 spectroscopic properties, which turn out to be quite sensitive to charge transfer state admixture, were studied theoretically and experimentally. These include gas-to-crystal shifts, site splittings, and Jahn-Teller interactions; comparison of calculated and experimental values clearly substantiate the conclusion that there is a strong influence of charge transfer states on the nature of the 5d3-t 2g 3 manifold. Finally, new data for the Γ8g (2 Eg ) and Γ6g (2 T 1g ) states at 1·2 μm are given, completing the data set for the t 2g 3 transitions of IrF6.

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