Uranyl dication, [UVI(O)2]2+, containing formal U–oxo triple bonds represents the most intensively investigated actinide-coordinated species exhibiting multiple bonds. Non-actinyl complexes exhibiting An–L multiple bonds are also known, with many examples reported for early actinides in oxidation states from +2 to +6. An-mono(oxo) molecular complexes featuring multiple bonds are less explored, with only a few examples known beyond uranium, such as the terminal neptunium(V)-mono(oxo) complex [NpVO(TrenTIPS)] featuring Np≡O triple bond. In this talk, I will present computational results comparing such complexes and focusing on the nature of their An–O and An–N bonding from the perspective of delocalized canonical molecular orbitals, orbital energy level diagrams, bond order indices, and more localized representations by employing electron density partitioning methodology. Specifically, I will describe two recently synthesized UVI-mono(oxo) complexes stabilized by four homoleptic tert-butyl/pyrrolidine/piperidine ligands, reported in our joint theoretical and experimental study in collaboration with the group of Prof. La Pierre. I will focus on the covalency of the U–O and U–N interactions, which exhibit multiple bond character, compare their bond polarization and hybridization, assess the involvement of 5f/6d orbitals, and discuss inverse-trans-influence effects.

Chemical bonding in actinide-mono(oxo) molecular complexes

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