Electronic, Magnetic, and Theoretical Characterization of (NH4)4UF8, a Simple Molecular Uranium(IV) Fluoride

Alexander T Chemey; Cristian Celis-Barros; Kevin Huang; Joseph M Sperling; Cory J Windorff; Ryan E Baumbach; David E Graf; Dayán Páez-Hernández; Michael Ruf; David E Hobart; Thomas E Albrecht-Schmitt

doi:10.1021/acs.inorgchem.8b02800

Electronic, Magnetic, and Theoretical Characterization of (NH₄)₄UF₈, a Simple Molecular Uranium(IV) Fluoride

Inorg Chem. 2019 Jan 7;58(1):637-647. doi: 10.1021/acs.inorgchem.8b02800. Epub 2018 Dec 20.

Affiliations

¹ Department of Chemistry and Biochemistry , Florida State University , Tallahassee , Florida 32306 , United States.
² National High Magnetic Field Laboratory , Florida State University , Tallahassee , Florida 32306 , United States.
³ Department of Physics , Florida State University , Tallahassee , Florida 32306 , United States.
⁴ Centro de Nanociencias Aplicadas, Facultad de Ciencias Exactas , Universidad Andrés Bello , Republica 275 , Santiago , Chile.
⁵ Bruker AXS , 5465 East Cheryl Parkway , Madison , Wisconsin 53711 , United States.

PMID: 30569705
DOI: 10.1021/acs.inorgchem.8b02800

Abstract

The simple system of tetraammonium octafluorouranate is employed to derive a fundamental understanding of the uranium-fluorine interaction. The structure is composed of isolated molecules, enabling a detailed examination of the U⁴⁺ ( f²) ion. Characterization of single-crystals by X-ray diffraction, absorption spectroscopy, and magnetic analysis up to 45 T is combined with extensive theoretical treatment by CASSCF. The influence of different active spaces and representations of the structure is examined in the context of the experimental evidence. The Interacting Quantum Atoms method (IQA) is used to examine the nature of the U-F bond, concluding that there is a non-negligible degree of covalent character (9% of the total bond energy) in [UF₈]^4-. For the structural and theoretical reasons discussed herein, it is proposed that the structure of (NH₄)₄UF₈ may be appropriately employed as a benchmark compound for future theoretical characterization of U(IV).