# Multiple oxidation states of uranium stabilized by an O,N,O-ligand

## TL;DR

This paper shows how a specific ligand can stabilize different uranium oxidation states, including U(IV), U(V), and U(VI), using various analytical techniques.

## Contribution

The study demonstrates the stabilization of three uranium oxidation states using an O,N,O ligand, expanding the understanding of uranium chemistry.

## Key findings

- U(IV)ExPh and UO2ExPh complexes were confirmed via X-ray diffraction and spectroscopy.
- Spectro-electrochemical analysis provided evidence for a stable U(V) species.
- Efforts to isolate U(III) from U(IV)ExPh were unsuccessful.

## Abstract

Elements of the 5f row maintain a wide variety of oxidation states that have been exploited in synthesis, catalysis, and separations. Herein, we describe the complexation of an O,N,O chelator, ExPh, with uranium in the (IV) and (VI) (uranyl) oxidation states. These two uranium complexes, U(iv)ExPh and UO2ExPh, respectively, were characterized in the solid state via single-crystal X-ray diffraction (SC-XRD) analysis. Electrochemical studies using cyclic voltammetry were employed to investigate the multiple redox events associated with the U(iv) complex. Spectro-electrochemical analysis of U(iv)ExPh provided spectroscopic evidence of a stable U(v) species. Chemical oxidation of U(iv)ExPh allowed isolation of the U(v) complex, U(v)ExPh. All three stable uranium complexes produced in this study were characterized via IR, UV-vis and NMR spectroscopies, and micro-spectrophotometry. On the other hand, efforts to reduce U(iv)ExPh to the corresponding U(iii) species or produce this putative complex directly from ExPh failed to yield an isolable product. The stabilization of three formal oxidation states of uranium, coupled with previous lanthanide-row results, paves the way for studies of ExPh and its analogues in minor actinide chemistry.

Complexes derived from H2ExPh reveal differences in ligand framework between lanthanide and uranium ions. Structures are overlaid on the cyclic voltammogram of U(iv)ExPh.