Halogen exchange reactions involving uranium-(V) and -(VI) halides

Abstract

The room temperature halogen exchange reactions of UF₅ with liquid BBr₃ or BCl₃ provide convenient new routes to α-UBr₅ and β-UCl₅, respectively. In both cases the yields are quantitative. Since the uranium pentahalides are the only involatile products of the reactions they are easily isolated. Reactions between BBr₃ and solid UCl₆ or UCl₅ also yield α-UBr₅ but in the presence of CH₂Cl₂, a new crystallographic modification, β-UBr₅, is produced. Interaction of UF₆ and BBr₃ yields either α- or β-UBr₅, depending on the conditions, but the products are usually contaminated with UBr₄. Liquid BCl₃ converts UO₂F₂ to α- or β-UCl₅, depending on the period of contact, whilst exposure of UO₂F₂ to gaseous BCl₃ yields UCl₆. X-Ray powder diffraction and vibrational spectroscopic data are reported for α- and β-UBr₅.