Facile Syntheses of pure Uranium(III) Halides: UF₃, UCl₃, UBr₃, and UI₃

Abstract

Herein we describe a convenient lab scale synthesis for pure and solvent‐free binary uranium(III) halides UCl 3 , UBr 3 , and UI 3 . This is achieved by the reduction of the respective uranium(IV) halides with elemental silicon in borosilicate ampoules at moderate temperature. The silicon tetrahalides Si X 4 formed as a side product are utilized for the removal of excess starting material via a chemical vapor transport reaction. The syntheses introduced herein avoid the need for pure metallic uranium and are based on uranium(IV) halides synthesized from UO 2 and the respective aluminum halides and purified by chemical vapor transport. These uranium(III) halides are obtained in single crystalline form. A similar reaction yields UF 3 as a microcrystalline powder. However, no beneficial transport reaction occurs with this halide. Also, a higher temperature has to be applied and steel ampoules have to be used. The identities and purity of the products were checked by powder X‐ray diffraction as well as IR spectroscopy. The synthesis of UI 3 enabled its crystal structure determination on single crystals for the first time. UI 3 crystallizes in the PuBr 3 structure type with space group type Cmcm and a = 4.3208(9), b = 13.923(3), c = 9.923(2) Å, V = 596.9(2) Å 3 , and Z = 4 at T = 100 K.