Structural, Electrochemical, and Magnetic Studies of Bulky Uranium(III) and Uranium(IV) Metallocenes

Michael A Boreen; Daniel J Lussier; Brighton A Skeel; Trevor D Lohrey; Fabian A Watt; David K Shuh; Jeffrey R Long; Stephan Hohloch; John Arnold

doi:10.1021/acs.inorgchem.9b02719

Structural, Electrochemical, and Magnetic Studies of Bulky Uranium(III) and Uranium(IV) Metallocenes

Inorg Chem. 2019 Dec 16;58(24):16629-16641. doi: 10.1021/acs.inorgchem.9b02719. Epub 2019 Nov 26.

Authors

Michael A Boreen^{1

2}, Daniel J Lussier^{1

2}, Brighton A Skeel¹, Trevor D Lohrey^{1

2}, Fabian A Watt³, David K Shuh², Jeffrey R Long^{1

2

4

5}, Stephan Hohloch³, John Arnold^{1

2}

Affiliations

¹ Department of Chemistry , University of California , Berkeley , California 94720 , United States.
² Chemical Sciences Division , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States.
³ University of Paderborn , Warburger Straße 100 , 33098 Paderborn , Germany.
⁴ Department of Chemical and Biomolecular Engineering , University of California , Berkeley , California 94720 , United States.
⁵ Materials Sciences Division , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States.

PMID: 31769982
DOI: 10.1021/acs.inorgchem.9b02719

Abstract

Addition of the potassium salt of the bulky tetra(isopropyl)cyclopentadienyl (Cp^iPr4) ligand to UI₃(1,4-dioxane)_1.5 results in the formation of the bent metallocene uranium(III) complex (Cp^iPr4)₂UI (1), which is then used to obtain the uranium(IV) and uranium(III) dihalides (Cp^iPr4)₂U^IVX₂ (2-X) and [cation][(Cp^iPr4)₂U^IIIX₂] (3-X, [cation]⁺ = [Cp*₂Co]⁺, [Et₄N]⁺, or [Me₄N]⁺) as mononuclear, donor-free complexes, for X^- = F^-, Cl^-, Br^-, and I^-. Interestingly, reaction of 1 with chloride and cyanide salts of alkali metal ions leads to isolation of the chloride- and cyanide-bridged coordination solids [(Cp^iPr4)₂U(μ-Cl)₂Cs]_n (4-Cl) and [(Cp^iPr4)₂U(μ-CN)₂Na(OEt₂)₂]_n (4-CN). Abstraction of the iodide ligand from 1 further enables isolation of the "base-free" metallocenium cation salt [(Cp^iPr4)₂U][B(C₆F₅)₄] (5) and its DME adduct [(Cp^iPr4)₂U(DME)][B(C₆F₅)₄] (5-DME). Solid-state structures of all of the compounds, determined by X-ray crystallography, facilitate a detailed analysis of the effect of changing oxidation state or halide ligand on the molecular structure. NMR spectroscopy, X-ray crystallography, cyclic voltammetry, and UV-visible spectroscopy studies of 2-X and 3-X further reveal that the difluoride species in both series exhibit properties that differ significantly from trends observed among the other dihalides, such as a substantial negative shift in the potential of the [(Cp^iPr4)₂UX₂] uranium(III/IV) redox couple. Magnetic characterization of 1 and 5 reveals that both compounds exhibit slow magnetic relaxation of molecular origin under applied magnetic fields; this process is dominated by a Raman relaxation mechanism.