Uranium (V) fluorides

Rhenium and uranium hexafluorides oxidise iodine in iodine pentafluoride at ambient temperature to give the I₂⁺ cation. With UF₆ additional reaction occurs to give β-uranium pentafluoride as one product (J.A. Berry, A. Prescott, D.W.A. Sharp, and J.M. Winfield, $\text{J. Fluorine Chem}$., 1977, $\text{10}$, 247). Further work on the latter reaction together with an electronic spectroscopic study of the oxidation of I₂ by phosphorus pentafluoride in IF₅, suggests that the fate of the I₂⁺ cation depends on the nature and quantity of the oxidising agent. Oxidation of I₂ by PF₅ can be conveniently followed by monitoring its visible spectrum. The reaction occurs over several hours and eventually an apparent equilibrium between I₂ and I₂⁺ results. Formation of I₂⁺UF₆^?is rapid and, with the mole ratio UF₆:I₂ > 10:1, UF₅ is precipitated rapidly from solution, I₂⁺ being oxidised further, apparently to IF₅. With a smaller UF₆:I₂ mole ratio UF₅ is contaminated by I₂, the latter is presumed to result from the disproportion-ation of an I^I or I^III fluoride.β-UF₅ is very soluble in acetonitrile and reacts with thallium(I) fluoride in this solvent to give Tl^IUF₆. It reacts with trimethyl(methoxo)silane to give (CH₃)₃SiF, U(OCH₃)₅, and an insoluble solid, believed to be a mixture of U^V methoxide, fluorides. Both reactions are conveniently followed by near i.r. spectroscopy.