ChemInform Abstract: KINETIC AND EQUILIBRIUM PARAMETERS FOR THE REACTION OF NEPTUNIUM(III) WITH TRIS(ETHYLENEDIAMINE)RUTHENIUM(III)

Abstract

The kinetic and equilibrium parameters for the reaction Np/sup 3 +/ + Ru(en)/sub 3//sup 3 +/ broken arrows Np/sup 4 +/ + Ru(en)/sub 3//sup 2 +/ have been determined in aqueous trifluoromethanesulfonate media. The observed forward rate constants (in M/sup -1/ s/sup -1/, ..mu.. = 1.00 M) are: 6.40 +- 0.23 (4.3/sup 0/C), 8.96 +- 0.38 (25/sup 0/C), and 9.78 +- 0.60 (40.3/sup 0/C). The enthalpy and entropy of the reaction are -12.6 +- 1.0 kcal/mol and -41.5 +- 3.3 eu. respectively. From these values, the E/sub f/ for Ru(en)/sub 3//sup 3+/2+/ in 1.0 M HCF/sub 3/SO/sub 3/ at 25/sup 0/C is calculated to be 0.167 V, in close agreement with the value of 0.172 V (..mu.. = 0.013 M) previously determined electrochemically. Activation parameters and the temperature dependence of the equilibrium quotients are similar to those determined for reactions of Np/sup 3 +/ with Ru(NH/sub 3/)/sub 6//sup 3 +/ and Ru(NH/sub 3/)/sub 5/H/sub 2/O/sup 3 +/. From the Marcus cross relation, the self-exchange rate for Ru(en)/sub 3//sup 2+/3+/ is calculated to be 5 times the corresponding rate for Ru(NH/sub 3/)/sub 6//sup 2+/3+/ in contrast to the value of 0.25 times this rate reported earlier. The relative exchange rate formore » these two species, as calculated from expected outer-sphere reorganization energy differences, is of the same order of magnitude and direction as we report.« less