Surprises in the Solvent-Induced Self-Ionization in the Uranium Tetrahalide UX₄ (X = Cl, Br, I)/Ethyl Acetate System

Abstract

The reaction of the uranium(IV) halides UCl 4 , UBr 4 , or UI 4 with ethyl acetate (EtOAc) leads to the formation of the complexes [UX 3 (EtOAc) 4 ][UX 5 (EtOAc)] (X = Cl, Br) or [UI 4 (EtOAc) 3 ]. Thus, both UCl 4 and UBr 4 show self-ionization in ethyl acetate to a distorted pentagonal bipyramidal [UX 3 (EtOAc) 4 ] + cation and a distorted octahedral [UX 5 (EtOAc)] − anion. Surprisingly, the chloride and bromide compounds are not isotypic. While [UCl 3 (EtOAc) 4 ][UCl 5 (EtOAc)] crystallizes in the orthorhombic crystal system, space group P 2 1 2 1 2 1 at 250 K, the bromide compound crystallizes in the monoclinic crystal system, P 12 1 / n 1 at 100 K. Unexpectedly, UI 4 does not show self-ionization but forms [UI 4 (EtOAc) 3 ] molecules, which crystallize in the monoclinic crystal system, P 2 1 / c , at 100 K. The compounds were characterized by single-crystal X-ray diffraction, IR, Raman, and NMR spectroscopy, as well as molecular quantum chemical calculations using solvent models.