Spectrophotometric and kinetic evidence is given for the formation of a complex, U204+3. The heat and entropy of formation from U02 + and U02+a were found to be -1.9 ± 0.3 kcal. mole"1 and -1 ± 1 cal. mole"1 deg."1 in perchlorate solutions 2.0 M in ionic strength. The complex has a characteristic absorption band at 7370 Á. (e 27 M~1 cm."1). The disproportionation rate of the complex is much lower than that of U02+, so U(V) solutions are greatly stabilized in the presence of U(VI). Rates of U(V) disproportionation were extrapolated to zero U(VI) to provide rate constants which are more reliable than previously available. Heats and entropies for the net activation process 2U02+ + H+ = [ -. • • 1 wire found to be 11.0 ± 0.4 kcal. mole"1 and -11.0 ± 1.5 cal. mole"1 deg."1.

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The kinetics of the reaction Pu(VI) + Fe(II) = Pu(V) + Fe(III) have been studied in acid perchlorate solutions between 0 and 25°. The rate is given byd[Pu(VI)]/dZ = (Pu(VI)] [Fe(II)] (A + (B + C[H+])-1l from 0.05 to 2.0 M HClCb at µ = 2.0. This rate law indicates the presence of a metastable binuclear intermediate, probably Pu(V)'Fe(III). Values of AH* and AS* have been computed for the formation of the three activated complexes required by the rate law. The effect of ionic strength between 0.05 and 2.0 M and the effect of 0.10 M Clwere determined.(1) This work was done under the auspices of the U. S. Atomic Energy Commission.

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