The strength of actinide-element bonds from the quantum theory of atoms-in-molecules

[AnX(3)](2)(mu-eta(2):eta(2)-N-2) (An = Th-Pu; X = F, Cl, Br, Me, H, OPh) have been studied using relativistic density functional theory. Geometric and vibrational data suggest that metal -> N-2 charge transfer maximises at the protactinium systems, which feature the longest N-N bonds and the smallest sigma(N-N), as a result of partial population of the N-N pi* orbitals. There is very strong correlation of the standard quantum theory of atoms-in-molecules (QTAIM) metrics bond critical point rho, del(2)rho and H and delocalisation indices with An-N and N-N bond lengths and sigma(N-N), but the correlation with An-N interaction energies is very poor. A similar situation exists for the other systems studied; neutral and cationic actinide monoxide and dioxides, and AnL(3+) and AnL(3)(3+) (L = pyridine (Py), pyrazine (Pz) and triazine (Tz)) with the exception of some of the del(2)rho data, for which moderate to good correlations with energy data are sometimes seen. By contrast, in almost all cases there is very strong correlation of interaction and bond energies with vertical bar Delta Q(An)(QTAIM)vertical bar, a simple QTAIM metric which measures the amount of charge transferred to or from the actinide on compound formation.