JRP CALL information
Supported By

European Commission

Short description of the work
We have previously shown that the tetraphenylimidophosphinate ligand (TPIP) stabilises neptunium and uranium exclusively in the +VI oxidation states including complete conversion from their +V states. (1,2) Moreover, TPIP is able to form oligomeric species assembled by actinyl Lewis acid base adducts (cation-cation interactions) for uranyl (VI) ions and preliminary evidence suggests such interactions occur in mixtures of neptunyl (VI) and uranyl (VI) (i.e. a mixed metal cation-cation aggregate). The study of such cation-cation interactions are extremely important in evaluating and developing new separation processes based on simplified versions of the PUREX process.

The JRP aimed to extend these studies to Pu(IV) and (VI) ions and investigate the redox stability of the complexes with TPIP and simple variants where the peripheral phenyl groups have been changed for electron donating groups (iPr) using the pooled facilities at CEA Marcoule (Atalante).
Three novel crystal structures were obtained with both phenyl (Pu(VI) and Pu(IV)) and iso-propyl (Pu(VI)) substituents on the TPIP ligand, allowing for a more detailed structural comparison and aiding assignment of the MS, IR and Raman spectra. ESI mass spectrometry confirmed the identity of the complexes. Tandem mass spectrometry (MS2) was used to assess further fragmentation and hence gave a qualitative assessment of the strength of ligand coordination. Raman and IR spectrometry were used in conjunction to assign bond stretches and to make comparisons between complexes. NMR spectroscopy yielded little useful information for the Pu(VI) complexes due to significant peak broadening caused by the paramagnetic effect. In contrast, the Pu(IV) complexes gave clean, simple NMR spectra that allowed for a full study, including 2D NMR experiments, which confirmed that the solid state structure was maintained in the solution state. UV-vis spectroscopy gave a clear indication of oxidation state and a distinctive shift in absorption wavelength upon complexation.
Mixed metal systems of uranyl(VI) or neptunyl(V) with plutonyl(VI) were also investigated in order to mimic the conditions that may be encountered under waste reprocessing conditions.

1. Redmond, M. P.; Cornet, S. M.; Woodall, S. D.; Whittaker, D.; Collison, D.; Helliwell, M.; Natrajan, L. S. Dalton Transactions 2011, 40, 3914
2. Woodall, S. D.; Swinburne, A. N.; lal Banik, N.; Kerridge, A.; Di Pietro, P.; Adam, C.; Kaden, P.; Natrajan, L. S. Chemical Communications 2015, 51, 5402

Main visitor contact data
Name: Kathryn George
Organisation: University of Manchester

JRP Identification
JRP nr: TALI-C05-04
JRP title: Investigating the oxidation state stability, preference and disproportionation mechanisms of imidodiphosphinate complexes of plutonium
JRP scope: Scope 1: Actinide separation chemistry

Visited Associated Pooled Facility
Visited APF during the stay: CEA - ATALANTE
Name of the APF Contact Person: Marie-Christine Charbonnel

Other APF and organisation involved in the JRP
Other organisations involved:
Other APF involved in the project:

Description of the work done at the associated pooled facility
Start date of the stay: 9/28/2015
End date of the stay: 12/4/2015
Quantity of access: 49
Access Unit: Days