Unraveling the highest oxidation states of actinides in solid-state compounds with a particular focus on plutonium

The nature and extent of the highest oxidation state (HOS) in solid-state actinide compounds are still unexplored compared with those of small molecules, and there is burgeoning interest in studying the actinide-ligand bonding nature in the condensed state. A comprehensive understanding of the electronic structure and unraveling the possibility of a HOS are of paramount importance in solid-state actinide chemistry. Here, we report the physical OS of the early to middle actinides (Th -> Cm) in solid-state compounds via a more rigorous quantum mechanical definition of OS under the DFT+ U theoretical frameworks for the first time. This work implies that the highest physical OS of the Pu solid ion is Pu-V in PuO2F and PuOF4, which can be achieved via tuning the ligand, thus improving our knowledge of oxidation states and chemical bonding in high OS solid-state compounds. We highlight the importance of ligand design in terms of the actinide HOS, employing a highly electronegative ligand and showing the capacity to form multiple bonds.