Experimental and Theoretical Approaches to Redox Innocence of Ligands in Uranyl Complexes: What is Formal Oxidation State of Uranium in Reductant of Uranyl(VI)?


Experimental and Theoretical Approaches to Redox Innocence of Ligands in Uranyl Complexes: What is Formal Oxidation State of Uranium in Reductant of Uranyl(VI)?

Takao, K.; Tsushima, S.; Ogura, T.; Tsubomura, T.; Ikeda, Y.

Redox behavior of [UO2(gha)DMSO]−/0 couple (gha = glyoxal bis(2-hydroxanil)ate, DMSO = dimethyl sulfoxide) in DMSO solution was investigated by cyclic voltammetry and UV-vis-NIR spectroelectrochemical technique, as well as density functional theory (DFT) calculations. [UO2(gha)DMSO] was found to be formed via one-electron reduction of UO2(gha)DMSO without any successive reactions. The observed absorption spectrum of [UO2(gha)DMSO], however, has clearly different characteristics from those of uranyl(V) complexes reported so far. Detailed analysis of molecular orbitals and spin density of the redox couple showed that the gha2− ligand in UO2(gha)DMSO is reduced to gha●3− to give [UO2(gha)DMSO] and the formal oxidation state of U remains unchanged from +6. In contrast, the additional DFT calculations confirmed that the redox reaction certainly occurs at the U center in other uranyl(V/VI) redox couples we found previously. The non-innocence of the Schiff base ligand in the [UO2(gha)DMSO]−/0 is due to the lower energy level of LUMO in this ligand relative to those of U 5f orbitals. This is the first example of the non-innocent ligand system in the coordination chemistry of uranyl(VI).

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Publ.-Id: 20073