Using Redox-Active Ligands to Generate Actinide Ligand Radical Species.

Using a redox-active dioxophenoxazine ligand, DOPO (DOPO = 2,4,6,8-tetra-tert-butyl-1-oxo-1H-phenoxazine-9-olate), a family of actinide (U, Th, Np, and Pu) and Hf tris(ligand) coordination compounds was synthesized. The full characterization of these species using 1H NMR spectroscopy, electronic absorption spectroscopy, SQUID magnetometry, and X-ray crystallography showed that these compounds are analogous and exist in the form M(DOPOq)2(DOPOsq), where two ligands are of the oxidized quinone form (DOPOq) and the third is of the reduced semiquinone (DOPOsq) form. The electronic structures of these complexes were further investigated using CASSCF calculations, which revealed electronic structures consistent with metals in the +4 formal oxidation state and one unpaired electron localized on one ligand in each complex. Furthermore, f orbitals of the early actinides show a sizable bonding overlap with the ligand 2p orbitals. Notably, this is the first example of a plutonium-ligand radical species and a rare example of magnetic data being recorded for a homogeneous plutonium coordination complex.