Uranium redox with complexes

Although the redox potentials for aqueous solution indicate that uranium(IV) should reduce plutonium(IV), anions and other complexing agents can change the potentials sufficiently that uranium(IV) and plutonium(IV) can coexist in solution (25). Since one of the products of photochemical reduction of uranyl by TBP is dibutyl phosphate (DBP), which complexes plutonium(IV) strongly, experiments were done to test the photochemically produced urani-um(IV) solutions as plutonium(IV) reductants (26). Bench-scale stationary tests showed these solutions to be equivalent to hydroxylamine nitrate solutions stabilized with hydrazine (27). 

CID of the uranium complex product of Eq. (32) first eliminates the acetaldehyde ligand and then the more strongly bound acetone ligand to give bare U02. The mechanism of this net reaction was not fuUy elaborated but was confirmed by deuterium substitution. That this process does not occur for the corresponding Ni, Co " ", Pb " ", or Ca + complexes substantiates the key role of the reduction of uranyl(VI) to uranyl(V), showing a correlation of gas-phase redox chemistry with the utility of solid uranium oxides as redox-active catalytic substrates. 

In the assessment of the refining performance of uranium, systematic data has been reported for the chemical properties of uranium complex in various alkali chlorides such as LiCl-RbCl and LiCl-CsCl mixtures [3-5], Information on the coordination circumstance of solute ions is also important since it should be correlated with stability. The polarizing power of electrolyte cations controls the local structure around neodymium trivalent Nd " " as an example of f-elements and the degree of its distortion from octahedral symmetry is correlated with thermodynamic properties of NdClg " complex in molten alkali chlorides [6]. On the other hand, when F coexists with Cr in melts, it is well-known that the coordination circumstances of solute ions are drastically changed because of the formation of fluoro-complexes [7-9]. A small amount of F stabilizes the higher oxidation states of titanium and induces a negative shift in the standard potentials of the Ti(IV)ITi(ni) and Ti(III)ITi(II) couples [7, 8], The shift in redox potentials sometimes causes specific electrochemical behavior, for example, the addition of F to the LiCl-KCl eutectic leads to the disproportionation of americium Am into Am " and Am metal [9],... 

The redox kinetics of the hexacyanoferrate(iii) reaction with uranium(iv) have been reported, the rate being dependent on [H+] with the hydrolysed complex, UOH +, as the reactive species. The rate law is of the form... 

Uranium (III) redox reactivity with small molecules always consists in the preliminary double reduction of the latter by two U(III) complexes. Thus, the reactivity concerns only U(IV) bimetallic complexes. DFT calculations can be used for this problem thanks to the recent development of 5f-in-core ECPs by Moritz et al. and a methodology to compute the preliminary redox step via the combination of small core and 5f-in-core calculations. Recent theoretical studies have mainly concerned the reduction of CO2 and CO, but attention has also to be paid to the reduction of CS2, COS, PhNCO, and PhNs, the C-C coupling of terminal bis-alkynes to form U(IV) vinyl complexes and the reduction of arenes. However, in order to have more elements to discuss about actinide properties, one must perform calculations at a multireference post Hartree-Fock level to take into account the important effect of electronic correlation in these systems however, there is the obstacle of the computational power to perform calculations of real systems at this level that stands still. 

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