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(3))(2)}(3)] with 2,2′-bipyrimidine (bpym) resulted in the formation of the bpym-bridged diuranium(iv) complex [{((Me(3)Si)(2)N)(3)U(IV)}(2)(μ-bpym(2−))], 1. Reduction with 1 equiv. KC(8) reduces the complex, affording [K(2.2.2-cryptand)][{((Me(3)Si)(2)N)(3)U}(2)(μ-bpym)], 2, which is best described as a radical-bridged U(III)–bpym˙(−)–U(III) complex. Further reduction of 1 with 2 equiv. KC(8), affords [K(2.2.2-cryptand)](2)[{((Me(3)Si)(2)N)(3)U(III)}(2)(μ-bpym(2−))], 3. Addition of AgBPh(4) to complex 1 resulted in the oxidation of the ligand, yielding the radical-bridged complex [{((Me(3)Si)(2)N)(3)U(IV)}(2)(μ-bpym˙(−))][BPh(4)], 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.