NUCLEAR MAGNETIC-RESONANCE STUDY OF THE KINETICS OF THE WATER EXCHANGE PROCESS IN THE EQUATORIAL POSITIONS OF URANYL COMPLEXES

The kinetics of the water exchange process in the equatorial positions of the aqua uranyl ion, mono-DMSO, mono-chloro, and mono-bromo complexes, have been studied by the NMR line broadening method in water-acetone mixtures. The measurements were made in the temperature region from 25 to -100°C and it was found that the relaxation process was controlled by water exchange below -50°C. The first-order rate constants for the exchange of the coordinated water molecules measured at -70°C for the various complexes are: kaq = 2.99 × 102 sec-1, kDMSO = 4.55 × 102 sec-1, kCl = 1.63 × 102 sec-1, and kBr = 2.65 × 102 sec-1. The values of the activation parameters are 9.9 ± 0.5 kcal mol-1 for ΔH≠ and 2.1 ± 2.6 e.u. for ΔS≠ for the aqua complex; considerably smaller values for ΔH≠ and ΔS≠ are obtained in the mono-substituted complexes. © 1979.