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(SiMe3)(2)}(3)] with 2,2'-bipyrimidine (bpym) resulted in the formation of the bpym-bridged diuranium(IV) complex [{((Me3Si)(2)N)(3)U-}2(IV)(mu-bpym(2-))], 1. Reduction with 1 equiv. KC8 reduces the complex, affording [K(2.2.2-cryptand)][{((Me3Si)(2)N)(3)U)(2)(mu-bpym)], 2, which is best described as a radical-bridged UIII-bpym center dot-U-III complex. Further reduction of 1 with 2 equiv. KC8, affords K(2.2.2-cryptand)[{((Me3Si)(2)N)(3)U-III}(2)(mu-bpym(2-))], 3. Addition of AgBPh4 to complex 1 resulted in the oxidation of the ligand, yielding the radical-bridged complex [{((Me3Si)(2)N)(3)U-IV}(2)(mu-bpym center dot-)][BPh4], 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.