We employ DFT and multireference methods to investigate geometric and electronic structures, chemical bonding interactions, redox properties, reactivity, and spectroscopic signatures of lanthanide (Ln) and actinide (An) coordination compounds holding potential for nuclear separation chemistry. The emphasis is placed on the role of f electrons in metal-ligand bonding and quantification of covalency in relation to the reactivity of such complexes. On one hand, we are interested in deciphering the fundamental aspects of the stabilization of highly reactive Ln and An complexes in extremely low oxidation states that could be tuned by the ligand capacity in storing the excess of the electron density at the metal center via back-donation, use of intercalated counterions, and electron withdrawing/donating groups. On the other hand, we aim to rationally design f-block molecular complexes in extremely high oxidation states that could be employed for oxidation-based separations. Our group is particularly interested in deciphering localized and multicenter interactions, covalency of metal-ligand bonding by assessing orbital overlap and energy degeneracy of metal and ligand orbitals, nature of redox events, electron correlation and spin-orbit coupling effects.