The present study was carried out to demonstrate that there is considerable ligandto-metal (LM) donation in PuO The open-shell occupation n open is critical to understand the multiplet structures that arise in spectroscopic measurements. For instance, the symmetries of the ground state of PuO 2 as Γ 1 and the first excited multiplet as Γ 4 (Bethe notation) are intimately related to the 5f open-shell configuration. Furthermore, n open = 4 is consistent with the absence of a permanent magnetic moment in the ground state of PuO 2 . On the other hand, the total charge of the Pu ions, which is related to n f and the effective occupation of the other Pu valence shells (6d, in particular), has significant consequences for the stability and reactivity of the compound as well as for spectroscopic parameters that probe shell occupations. The present study aims at a clear distinction between n open and n f , such that the findings of Reference 7 do not lead to attempts to re-classify the Pu oxidation number (ON) in PuO 2 as +III, which we consider counterproductive.