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

Abstract

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)2N)3UIV}2(μ-bpym2−)], 1. Reduction with 1 equiv. KC8 reduces the complex, affording [K(2.2.2-cryptand)][{((Me3Si)2N)3U}2(μ-bpym)], 2, which is best described as a radical-bridged UIII-bpym˙−-UIII complex. Further reduction of 1 with 2 equiv. KC8, affords [K(2.2.2-cryptand)]2[{((Me3Si)2N)3UIII}2(μ-bpym2−)], 3. Addition of AgBPh4 to complex 1 resulted in the oxidation of the ligand, yielding the radical-bridged complex [{((Me3Si)2N)3UIV}2(μ-bpym˙−)][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.