Structural and spectroscopic studies of the complex [BuMeIm]2[UCl6] in the solid state and in hydrophobic room temperature ionic liquid [BuMeIm][Tf2N]

The complex [BuMeIm]2[UCl6] was characterized in the solid state and in a solution of [BuMeIm][Tf2N] room temperature ionic liquid using single-crystal XRD, EXAFS, visible absorption spectroscopy and NMR techniques.The structure of solid [BuMeIm]2[UCl6] contains two crystallographically independent formula units (U(1) and U(2)).The U–Cl distances in Click to view the MathML source anions range from 2.576(6) to 2.638(4) Å, the average values being 2.621(6) and 2.601(8) Å for U(1) and U(2), respectively.The BuMeIm+ cations have four different conformations of C4H9 chains.The shortest distances between the centres of the five-member rings of the BuMeIm+ cations and U atoms of [UCl6]2− anions are in the range 5.53–4.90 Å.Single-crystal XRD data reveal the existence of a hydrogen bond between the most acidic H atom of the imidazolium ring (C2) and the chloride anion of the Click to view the MathML source octahedron, with the shortest distance Clcdots, three dots, centeredH(C2) equal to 2.57 Å.Quantitative EXAFS measurements indicate that the octahedral complex Click to view the MathML source(RU–Cl = 2.632(2) Å) is the predominant chemical form of U(IV) in [BuMeIm][Tf2N] solution.Visible absorption spectroscopy and 1H NMR spectroscopy confirm the existence of hydrogen bonding between theClick to view the MathML source anion and the acidic proton of the BuMeIm+ cation in RTIL solution, similar to that in the solid state.