JRP CALL information
Supported By

European Commission

Short description of the work
The project undertaken was a continuation of a previous grant to visit JRC-ITU in Actinet 6. The ultimate goal is the better understanding of the interactions between actinyl cations and with other metal ions in nuclear waste by synthesising model systems held together by cation-cation interactions (CCI). In the short term, studying the formation and stability of actinide metal-oxo bonds in discrete molecules also offers the fascinating potential to make new single molecule magnets with enhanced properties. We have previously developed a readily-made Schiff-base polypyrrolic ligand (H4L; L= Pacman) which allows the stabilisation of the uranyl(V) monocation and its subsequent derivatisation by oxo-metalation.

The work carried out at JRC-ITU was the synthesis of low-valent uranium and neptunium starting materials for reductive metalation of the uranyl dication in the Pacman ligand [(UO2)(H2L)]. Prior to the visit, the mono-oxo functionalised potassium uranyl(V) Pacman [(K)(UO2)(H2L)] had been synthesised at the University of Edinburgh to be used as a starting material for subsequent salt metathesis reactions.

The synthesis of the neptunium starting material required the set-up of a suitable apparatus for carrying out the reaction in an alpha glove-box under air- and moisture free conditions. At JRC-ITU, using Schlenk and glove box techniques, neptunium metal and iodine were reacted in dioxane as the solvent to synthesise neptunium(III) iodide as the dioxane adduct by ultrasonication and subsequent stirring over several days at room temperature. Several crystallisation methods have been attempted, however, to date the compound has not been isolable in crystalline form with crystals that are amenable to investigation by single crystal X-ray diffraction. U(IV) in the form of Cp3UCl (Cp = cyclopentadienyl), which we were provided with, was reduced to U(III) by treatment with sodium amalgam in diethyl ether at room temperature over several days, yielding upon recrystallization solvent-free Cp3U. This compound was subsequently analysed using single crystal X-Ray diffraction to verify its composition. This was used to reductively functionalise uranyl(VI) Pacman [(UO2)(H2L)] in tetrahydrofuran at -78 °C to afford [(Cp3U)(UO2)(H2L)]. This was carried out as a test reaction prior to repeating the reaction with the neptunium analogue, to ensure that the synthetic procedures were sound. This contains a Cp3U(IV)-O-U(V)=O motif; in addition to being a good model for uranium-CCI complexes, it is a 5f2-5f1 system, so it is potentially a magnetically interesting molecule in its own right. It is currently being investigated for magnetic and electronic properties.

Additionally we performed UV-Vis spectroscopic analyses on the product of the salt metathesis reaction between the already-reduced potassium salt of uranyl(V) Pacman [(K)(UO2)(H2L)] and one equivalent of Cp3UCl. This was anticipated to afford the same product as above, [(Cp3U)(UO2)(H2L)]. The UV-Vis measurement indicated the formation of a uranium(IV)-uranyl(V) system, however, partial decomposition of the sample did not allow a conclusive confirmation of the identity of the product.

Within the allocated period of the Talisman project we were able to start on the next desired reaction of uranyl Pacman [(UO2)(H2L)] with one or two equivalents of a low-valent neptunium starting material (NpI3, Cp3Np). The products of these reactions are about to be investigated.

To conclude so far, we have been able to synthesise NpI3 as the dioxane adduct and solvent-free Cp3U. Cp3U was crystallographically characterised and used as a reductant for reductive metalation of uranyl Pacman [(UO2)(H2L)] to afford [(Cp3U)(UO2)(H2L)] which is currently still being investigated for its molecular, electronic and magnetic properties. Previously synthesised potassium uranyl(V) Pacman [(K)(UO2)(H2L)] showed upon addition of one equivalent Cp3UCl the formation [(Cp3U)(UO2)(H2L)]. Conclusive remarks with respect to the reductive potential of low-valent neptunium in reactions with uranyl(VI) Pacman [(UO2)(H2L)] currently remain open.

Main visitor contact data
Name: Markus ZEGKE
Organisation: The University of Edinburgh

JRP Identification
JRP nr: TALI-C02-07
JRP title: Covalency and CCI studies through reduction and metal ‐ metal interactions in transuranic molecules
JRP scope: Scope 3: Actinide materials

Visited Associated Pooled Facility
Visited APF during the stay: JRC-ITU - Labs & Hot-cells
Name of the APF Contact Person: Roberto Caciuffo

Other APF and organisation involved in the JRP
Other organisations involved: The University of Edinburgh
Other APF involved in the project:

Description of the work done at the associated pooled facility
Start date of the stay: 11/18/2013
End date of the stay: 12/13/2013
Quantity of access: 20
Access Unit: Days