Coordination chemistry of N-Donor Ligands with early Actinides

The development and investigation of N-donor ligands e.g. for actinide / lanthanide separation is an ongoing field of study, in particular with respect to understanding the structure-property-relationship.
In this context we have been exploring the coordination chemistry of the early actinides (Th – Am) with tridentate chelating ligands containing pyridine and bipyridine moieties.
Ligands 1 and 2 were successfully used for complexation with trivalent lanthanides.
Encouraged by these results, we have been focusing on their coordination chemistry with tri- and tetravalent early actinides. We aim to understand the reactivity of these ligands that exploit the unique electronic structure of the early 5f-elements.
The synthesis of such complexes was carried out in acetonitrile with recrystallization from methanol.
For instance, the synthesized U(IV) complex of 1a which was characterized by single crystal XRD revealed a nine-fold coordinated uranium center. In contrast to the nine-fold Ln(III) complex which exhibits a ligand to metal ratio of 3:1 the U(IV) complex shows a 2:1 ratio with additional methanolato and iodo ligands for charge compensation.
Expanding the series to the tri- and tetravalent transuranic metals and characterizing the obtained complexes both structurally and spectroscopically will help to elucidate the differences between the coordination behavior of the lanthanides compared to the actinides.