High-valent late-transition-metal fluorides are among the strongest known oxidizing agents. IrF₆ and PtF₆, in particular, are used as high-potential oxidizers. However, there is a lack of data on the molecular structure and spectroscopic properties of low-valent iridium fluorides, and a systematic investigation that considers all possible iridium fluoride species had not been reported so far.

Sebastian Riedel, Freie Universität Berlin, Germany, and colleagues, have synthesized and characterized molecular iridium fluorides, combining matrix-isolation spectroscopy and theoretical studies. For the first time, the whole series of IrF_n (n = 1-6) has been investigated. The team studied the photo-initiated defluorination of iridium hexafluoride (IrF₆) in neon and argon matrices at 6 K. The photoproducts were characterized by infrared (IR) and UV-Vis spectroscopy as well as quantum-chemical calculations.

The primary photoproducts obtained from IrF₆ after UV irradiation (λ = 365 nm) are iridium pentafluoride (IrF₅) and iridium trifluoride (IrF₃). Longer irradiation of the same matrix (λ = 278 nm) gave iridium tetrafluoride (IrF₄) and iridium difluoride (IrF₂) by Ir−F bond cleavage or F₂ elimination. In addition, IrF₅ can be transformed back to IrF₆ by the addition of an F atom under blue-light irradiation (λ = 470 nm). Laser irradiation (λ = 266 nm) of IrF₄ also generated IrF₆, IrF₅, IrF₃, and IrF₂. The team found that spin-orbit coupling effects in IrF₅ lead to a triplet ground state with C_4v symmetry—a rare example of a molecule in which spin-orbit coupling has a significant influence on the structure.

• Investigation of Molecular Iridium Fluorides IrF_n (n = 1‐6): A Combined Matrix‐Isolation and Quantum‐Chemical Study,
  Sebastian Hasenstab-Riedel, Yan Lu, Yetsedaw A. Tsegaw, Artur Wodyński, Lin Li, Helmut Beckers, Martin Kaupp,
  Chem. Eur. J. 2022.
  https://doi.org/10.1002/chem.202104005