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.