Theoretical description of metal-ligand bonding within f-element complexes: A successful and necessary interplay between theory and experiment

The quantum chemical study presented here shows various aspects of the bonding of lanthanide (La3+, Gd (3+)) and actinide (U3+, AM(3+), CM3+) ions with N-heterocyclic ligands (polyazines, BTP: bis(1,2,4-triazinyl)-2,6-pyridine). Several families of complexes, differing by their coordination sphere, have been examined. Clearly, the lanthanide complexes always show a purely ionic bonding. The behaviour of U(III) is also well defined with a more or less strong backbonding interaction whatever the complex is. In contrast, the heavy actinides (Am3+ and Cm3+) are changeable, with a weak covalent character, going from donation to backdonation, depending on the coordination sphere of the complex.