Jahn-Teller Effect in the Eg Vibrational Mode of Hexafluoride Molecules. The Infrared Spectra of RuF6 and RhF6

Abstract

The infrared spectra of RuF₆ and RhF₆ are reported and are interpreted in terms of a regular octahedral structure, point group O_h. The spectrum for RuF₆ shows fewer bands than any of the known hexafluoride molecules, presumably owing to a Jahn‐Teller effect. The fundamental vibrational frequencies (cm⁻¹) for RuF₆ are v₁=675, v₃=735, v₄=275, v₅=262; for RhF₆, v₁=634, v₂=595, v₃=724, v₄=283, v₅=269, and v₆=192; for RuF₆ v₂ is estimated to be 573. A broad band arising from an electronic transition in RuF₆ is also observed with maxima at 1950 and 1400 cm⁻¹. The symmetry requirements for a Jahn‐Teller effect in a regular octahedral hexafluoride molecule are summarized. The evidence for a Jahn‐Teller effect in the E_g mode for hexafluoride molecules is reviewed. An analogous effect is not observed for the F_2g mode although it is symmetry allowed. Comparison of band widths for (v₁+v₃) and (v₂+v₃) permits the following estimates of the Jahn‐Teller splittings (cm⁻¹) for the E_g mode: TcF₆=80, ReF₆=25, and OsF₆=54. RhF₆, like IrF₆, does not show a Jahn‐Teller effect of comparable magnitude, presumably because of the ``spin character'' of its Γ₈ electronic ground state. The corresponding effect for RuF₆ is relatively larger and cannot be evaluated in this way because the band (v₂+v₃) is so broadened as to make it extremely difficult to characterize.