Identification of the +2 Oxidation State for Uranium in a Crystalline Molecular Complex, [K(2.2.2-Cryptand)][(C5H4SiMe3)3U]

Abstract

Flash reduction of Cp′₃U (Cp′ = C₅H₄SiMe₃) in a column of potassium graphite in the presence of 2.2.2-cryptand generates crystalline [K(2.2.2-cryptand)][Cp′₃U], the first isolable molecular U²⁺ complex. To ensure that this was not the U³⁺ hydride, [K(2.2.2-cryptand)][Cp′₃UH], which could be crystallographically similar, the hydride complex was synthesized by addition of KH to Cp′₃U and by reduction of H₂ by the U²⁺ complex and was confirmed to be a different compound. Density functional theory calculations indicate a 5f³6d¹ quintet ground state for the [Cp′₃U]⁻ anion and match the observed strong transitions in its optical spectrum.