"High-Valent f-element Coordination Complexes: Connecting Quantum Chemical Modeling to Measured Properties"
The electronic structure of the coordination chemistry of the 4f-elements typically involves metal-centered valence orbitals and weak ligand fields. However, stabilizing unusually high formal oxidation states requires designing ligands that fall outside this classical paradigm. This talk explores how a combined use of density functional theory and multiconfigurational methods can provide insights into recently synthesized high-valent praseodymium complexes. By characterizing the pseudo-tetrahedral [Pr(IV)(NPtBu3)3] complex, the interplay between crystal field splitting and spin-orbit coupling is explored. Moreover, this complex has an accessible Pr5+/4+ redox couple allowing it to be oxidized to form a molecular praseodymium complex in the formal +5 oxidation state, specifically [Pr(V)(NPtBu3)3]+, where a multiconfigurational singlet ground state resulting from an inverted ligand field. To place the electronic structure of the 4f species in context, this talk will draw parallels to the inverted ligand fields observed in high-valent transition metal chemistry, specifically , Cu(II) species. The comparison between the 4f and 3d metals will lead into a conversation about the high-valent actinides. Specifically, the dramatic change in molecular geometry observed for a uranium(V) oxo complex. By invoking the concept of an “inverse trans influence”, we can understand the different behavior with soft-donor sulfur groups compared to the analogous oxo-donating ligands. This final section of the talk will focus on how experimental observables like structure and spectra cannot always be used alone to assign bonding but provide important metrics that, only when computed, can be used to provide the full picture of what stabilizes the structure.