Syntheses, Single-Crystal Structures, and Structural Chemistry of Hexafluoridouranates(V), <i>M</i>UF₆ (<i>M</i> = Li–Cs, Ag, Tl, H₃O), and the Dodecafluoridodiuranate(V) Ba[U₂F₁₂]·1.36HF

We present the syntheses of the hexafluoridouranates(V) <i>M</i>UF₆ (<i>M</i> = Li-Cs, Ag, Tl, H₃O) and of the dodecafluoridodiuranate(V) Ba[U₂F₁₂]·1.36HF. With the exception of AgUF₆ and H₃OUF₆, all compounds were synthesized by reacting the respective metal fluorides with β-UF₅ in anhydrous hydrogen fluoride (aHF). AgUF₆ was obtained as a side product in the oxidation of Ag powder with UF₆ under a CO atmosphere, while H₃OUF₆ was obtained from the controlled hydrolysis of β-UF₅ with SiO₂ in aHF. For this hydrolysis, silica glass wool proved to be the superior choice of SiO₂. X-ray diffraction experiments on single crystals of the compounds as well as on polycrystalline samples allowed the unambiguous determination of their crystal structures, clarifying previously published structure models that were based on only powder X-ray diffraction. The structural chemistry of these compounds is discussed. In the case of LiUF₆, NaUF₆, and H₃OUF₆, molecular UF₆^- anions are observed in the solid state, while one-dimensional infinite strands of _∞¹{[UF_4/1F_4/2]^-} anions are present in the crystal structures of KUF₆, RbUF₆, TlUF₆, and AgUF₆. The dodecafluoridodiuranate(V) Ba[U₂F₁₂]·1.36HF is the second example of a compound containing the peculiar [U₂F₁₂]^2- anion. Its U atoms show a coordination number of seven in a capped trigonal prismatic coordination sphere, and these prisms share a common edge. In contrast to the Sr homologue, the Ba compound contains HF molecules of crystallization.