Magnetic Exchange Coupling in Chloride-Bridged 5f-3d Heterometallic Complexes Generated via Insertion into a Uranium(IV) Dimethylpyrazolate

The observation of slow magnetic relaxation in certain high-spin molecules has sparked a search for new systems capable of supporting higher relaxation barriers.1 Recently, a number of such “single-molecule magnets ” have been discovered in which lan-thanide ions contribute substantially or entirely to the magnetic anisotropy responsible for the relaxation barrier.2 Unfortunately, high spin ground states that are well-isolated in energy are difficult to achieve in species of this type, because the contracted 4f orbitals of lanthanide ions have little overlap with bridging ligand orbitals, leading to magnetic exchange constants of only a few wavenumbers at best.3 In contrast, the 5f orbitals of actinide ions can exhibit an increased radial extension relative to the core electron density,4 potentially enabling stronger magnetic coupling via superexchange. To date, however, there are only a few cases of actinide-containing molecules for which the presence of magnetic exchange couplin