Reactivity between the trivalent lanthanides and actinides with ligands has been a long-discussed topic in f-element chemistry. Some of the trivalent lanthanides and actinides are similar in size as well as in their chemical properties making them difficult to separate. Though bonding involving actinide-ligand covalency has been established, there was no accurate thermodynamic data that can differentiate between the lanthanides and actinides. A series of trivalent lanthanides and actinides were synthesized with tertiary butyl-phosphinodiboronate, ([M2(H3BPtBu2BH3)6], M=La3+, Ce3+, Pr3+, Nd3+, U3+) complexes. In the solid state, these species form dimeric structures but are observed by NMR to depolymerize in solution. The U-B bond distance is shorter than in analogous Ln-B bonds. This was then shown to impact the deoligomerization reactivities and corresponding enthalpies and free energies of reaction. Density functional theory (DFT) is used to calculate thermodynamic values which are in very good agreement with experiment. Moreover, QTAIM analysis supports that the interaction along the U-B bond distance is more covalent than in the lanthanides.

Quantitative bond analysis between the trivalent lanthanide and uranium phosphinodiboronate complexes using DFT

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