Anomalous magnetism of uranium(IV)-oxo and -imido complexes reveals unusual doubly degenerate electronic ground states

Uranium–nitride chemistry: uranium–uranium electronic communication mediated by nitride bridges

“…These data are characteristic of uranium( iv ) ions that are bonded to charge-loaded, strong point donor ligands that includes oxo, imide, and nitride linkages. 15 The magnetic data support the uranium( iv ) formulations of 2 and 5, though the large low-temperature effective magnetic moments suggest that 2 and 5 do not adopt the usual magnetic singlet ground state of uranium( iv ) (whose low-temperature magnetic moment would usually be essentially zero but in reality ∼0.3 μ B per U ion due to temperature-independent paramagnetism), but instead exhibit doubly degenerate ground states. 15 This is consistent with the strong point charge nature of a nitride, and also further demonstrates that such ligands result in the effective symmetry of the crystal field that they enforce dominating over what would otherwise be the spin–orbit coupled nature of the ground multiplet.…”

Hyperion: A New Computational Tool for Relativistic Ab Initio Hyperfine Coupling

“…Overall, it appears that minimal CASSCF-SO provides the most balanced model for the hyperfine structure of TMs, with errors around 25%. Approaches that include more correlation effects can theoretically improve the accuracy of the FC+SD term; in practice, however, the state-averaging formalism employed in CASSCF-SO, combined with the number of optimized spin-free stateswhich are likely characterized by different dynamical correlation effectsworsen the quality of the SO-coupled wave functions, , which propagates to the computed HFCCs.…”

Unprecedented pairs of uranium (iv/v) hydroxido and (iv/v/vi) oxido complexes supported by a seven-coordinate cyclen-anchored tris-aryloxide ligand

“…Especially the low-temperature magnetic moment of 2 is relatively high for uranium(IV) complexes with its 5f 2 electronic configuration and its, presumably, 3 H4 non-magnetic ground state, 59 suggests either a high contribution of temperature-independent paramagnetism (TIP) at low temperatures or an unusual pseudo-doublet ground state. 60,61 Tetravalent complexes of the tacn-based tris-aryloxide ligand system, for instance, often possess low-temperature moments down to approx. 0.3 µB.…”