Carbon-13 NMR characterization of actinyl(VI) carbonate complexes in aqueous solution

The uranyl(VI) carbonate system has been re-examined using 13C NMR of 99.9% 13C-enriched UVIO2 (13CO3)34- in millimolar concentrations. By careful control of carbonate ion concentration, we have confirmed the existence of the trimer, and observed dynamic equilibrium between the monomer and the timer. In addition, the ligand exchange reaction between free and coordinated carbonate on PuVIO2(13CO3)34- and AmVIO2(13CO3)34- systems has been examined by variable temperature 13C NMR line-broadening techniques 13C NMR line-broadening techniques. A modified Carr-Purcell-Meiboom-Gill NMR pulse sequence was written to allow for experimental determination of ligand exchange parameters for paramagnetic actinide complexes. Preliminary Eyring analysis has provided activation parameters of ΔGdouble-dagger295 = 56 kJ/M, ΔHdouble-dagger = 38 kJ/M, and ΔSdouble-dagger = -60 J/M-K for the plutonyl triscarbonate system, suggesting an associative transition state for the plutonyl (VI) carbonate complex self-exchange reaction. Experiments for determination of the activation parameters for the americium (VI) carbonate system are in progress