Assembling diuranium complexes in different states of charge with a bridging redox-active ligand.

Radical-bridged diuranium complexes are desirable for their potential high exchange coupling and single molecule magnet (SMM) behavior, but remain rare. Here we report for the first time radical-bridged diuranium(iv) and diuranium(iii) complexes. Reaction of [U{N(SiMe)}] with 2,2'-bipyrimidine (bpym) resulted in the formation of the bpym-bridged diuranium(iv) complex [{((MeSi)N)U}(μ-bpym)], 1. Reduction with 1 equiv. KC reduces the complex, affording [K(2.2.2-cryptand)][{((MeSi)N)U}(μ-bpym)], 2, which is best described as a radical-bridged U-bpym˙-U complex. Further reduction of 1 with 2 equiv. KC, affords [K(2.2.2-cryptand)][{((MeSi)N)U}(μ-bpym)], 3. Addition of AgBPh to complex 1 resulted in the oxidation of the ligand, yielding the radical-bridged complex [{((MeSi)N)U}(μ-bpym˙)][BPh], 4. X-ray crystallography, electrochemistry, susceptibility data, EPR and DFT/CASSCF calculations are in line with their assignments. In complexes 2 and 4 the presence of the radical-bridge leads to slow magnetic relaxation.