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