Looking at the contributions given in Table 4 and Table S6 in the ESI,
it can be noted that in complex 1 the contribution to the bond
order coming from σ-NLMOs ranges from 70-91% denoting a high
predominance of the σ-character of the bond. On the other hand, for
complex 2 a similar predominance for
Bk–OCO3 bonds is observed (74-87%) but significantly
deviates for Bk–OH bonds (56%). This means that the bond order in the
latter bonds is increased by π contributions.