Photochemical Synthesis and Characterization of Xenon(VI) Hexafluoridomanganates(IV)

Reactions between XeF₂, MnF₃ and UV-irradiated elemental F₂ in anhydrous HF have yielded [XeF₅]₂[MnF₆] and XeF₅MnF₅; meanwhile, [XeF₅]₄[Mn₈F₃₆] has been observed as a minor phase upon the crystallization of the product obtained by fluorination of an n(XeF₂)/n(MnF₃) = 1:3 mixture in the presence of an UV source. The crystal structure of [XeF₅]₂[MnF₆] is isotypic with the known [XeF₅]₂[PdF₆]. Its asymmetric structural unit consists of two crystallographically unique [XeF₅]⁺ cations and a [MnF₆]^2– anion. The single-crystal structure determination of XeF₆·2MnF₄ reveals that it is better formulated as [XeF₅]₄[Mn₈F₃₆]. Discrete octameric [Mn₈F₃₆]^4– anions are built from eight MnF₆ octahedra, each sharing three vertices, in the shape of a ring, which is different from the previously known cubic [Ti₈F₃₆]^4– anion. The main structural feature of the anionic part of the crystal structure of [XeF₅][MnF₅] (determined from both X-ray single-crystal and synchrotron X-ray powder diffraction data) is infinite zigzag chains of distorted MnF₆ octahedra that share cis vertices. [XeF₅][MnF₅] is paramagnetic in the 296–200 K temperature range, with a Curie constant of C = 1.87 emu K mol^–1 (µ_eff = 3.87 µ_B) and a Curie–Weiss temperature of θ = –9.3 K. Below 100 K, there is weak antiferromagnetic coupling between the Mn^IV ions, with a coupling constant of J = –1.3 cm^–1. Raman spectra showed that [XeF₅]₂[MnF₆] decomposes at ambient temperature in a He–Ne laser beam (power > 1.7 mW) to [XeF₅][MnF₅], with further decomposition to MnF₃.