Contributions from Electrons of Valence Molecular Orbitals to the Population of Bonds in AnO2 Complexes (An = Th–Lr)

Relativistic discrete variation is used to obtain the dependence of contributions from electrons of the valence molecular orbitals (MOs) of AnO₂ (An = Th–Lr) to a population of bonds (according to Mulliken) on atomic number Z. It is noted that the electrons of outer valence MOs (OVMO) strengthen a bond, while those of inner valence MOs (IVMO) weaken a bond by an average of one third. The efficiency of the formation of IVMOs observed in experiments characterizes the uniqueness of the chemical bond of actinide dioxides. The effect the electrons of valence MOs have on a covalent bond is greatly reduced and becomes more ionic when Z is raised. Strong covalence effects are observed in AnO₂ due to An 6d, An 6p, and An 5f AOs overlapping with ligand orbitals.