Investigation of Molecular Iridium Fluorides IrF_n (n=1-6): A Combined Matrix-Isolation and Quantum-Chemical Study

The photo-initiated defluorination of iridium hexafluoride (IrF₆ ) was investigated in neon and argon matrices at 6 K, and their photoproducts are characterized by IR and UV-vis spectroscopies as well as quantum-chemical calculations. The primary photoproducts obtained after irradiation with λ=365 nm are iridium pentafluoride (IrF₅ ) and iridium trifluoride (IrF₃ ), while longer irradiation of the same matrix with λ=278 nm produced iridium tetrafluoride (IrF₄ ) and iridium difluoride (IrF₂ ) by Ir-F bond cleavage or F₂ elimination. In addition, IrF₅ can be reversed to IrF₆ by adding a F atom when exposed to blue-light (λ=470 nm) irradiation. Laser irradiation (λ=266 nm) of IrF₄ also generated IrF₆ , IrF₅ , IrF₃ and IrF₂ . Alternatively, molecular binary iridium fluorides IrF_n (n=1-6) were produced by co-deposition of laser-ablated iridium atoms with elemental fluorine in excess neon and argon matrices under cryogenic conditions. Computational studies up to scalar relativistic CCSD(T)/triple-ζ level and two-component quasirelativistic DFT computations including spin-orbit coupling effects supported the formation of these products and provided detailed insights into their molecular structures by their characteristic Ir-F stretching bands. Compared to the Jahn-Teller effect, the influence of spin-orbit coupling dominates in IrF₅ , leading to a triplet ground state with C_4v symmetry, which was spectroscopically detected in solid argon and neon matrices.