Conclusions

Through this study, we have shown some aspects of the chemistry of Bk(IV) carbonate and carbonate-hydroxide complexes based on experimental studies reported three decades ago. The covalent character of the bonds has been deconvoluted by different approaches utilizing correlated wavefunctions showing variations in the bond due to increased orbital overlap as in the case of Bk–OH bonds. This implies stronger coordination of hydroxyl ions over the carbonate ions, which could be related to the displacement of carbonate ions from the first sphere of coordination of Bk(IV) in basic solutions. The role of the symmetry in the strength of the bond has also been exposed by the weakening of the bond of the carbonate opposite to OH(1).
The importance of integrating multiple theoretical approaches, even those seemingly opposed in nature, as the non-overlapping picture of the atoms in molecules with the overlap-based theory of NBO, is crucial in obtaining a full picture of these elusive actinide systems. Furthermore, using the concept of overlapping atoms, the increased orbital overlap in Bk–OH bonds leaves the question open as to if covalency in heavy elements is driven solely by energy orbital matching.19,28