Multiple oxidation states of uranium stabilized by an O,N,O-ligand
Gabriel J Juarez1, Harris E Mason2, Daniel N Mangel1
1Department of Chemistry, The University of Texas at Austin 105 East 24th Street, Stop A5300 Austin Texas 78712-1224 USA sessler@cm.utexas.edu.
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.
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