Electron transfer in neptunyl(VI)-neptunyl(V) complexes in solution.
The rates and mechanisms of the electron self-exchange between Np(V) and Np(VI) in solution have been studied with quantum chemical methods and compared with previous results for the U(V)-U(VI) pair. Both outer-sphere and inner-sphere mechanisms have been investigated, the former for the aqua ions, the latter for binuclear complexes containing hydroxide, fluoride, and carbonate as bridging ligand. Solvent effects were calculated using the Marcus equation for the outer-sphere reactions and using a nonequilibrium PCM method for the inner-sphere reactions. The nonequilibrium PCM appeared to overestimate the solvent effect for the outer-sphere reactions. The calculated rate constant for the self-exchange reaction NpO2(+)(aq) + NpO2(2+)(aq) right harpoon over left harpoon NpO2(2+)(aq) + NpO2(+)(aq), at 25 degrees C is k = 67 M(-1) s(-1), in fair agreement with the observed rates 0.0063-15 M(-1) s(-1). The differences between the Np(V)-Np(VI) and the U(V)-U(VI) pairs are minor.
Macak
Peter
P
Theoretical Chemistry, The Royal Institute of Technology, AlbaNova University Center, S-10691 Stockholm, Sweden. pemac@theochem.kth.se
Fromager
Emmanuel
E
Privalov
Timofei
T
Schimmelpfennig
Bernd
B
Grenthe
Ingmar
I
Wahlgren
Ulf
U