Structure and Magnetic Properties of a Series of Uranium Bis-Siloxide Complexes

Despite their synthetic interest and potential attractive properties, the preparation of heteroleptic U(III) complexes containing monodentate ligands remains challenging. Here we report the synthesis, structure and magnetic properties of three heteroleptic U(III) complexes containing two siloxide donors in the coordination sphere. The bis-siloxide monoiodide complex [U(OSi(OtBu)3)2I(thf)3], 1 provides a very attractive precursor for accessing heteroleptic complexes and rationally modify the binding angle between the two strongly donating siloxide ligands. Here we reacted 1 with macrocyclic ligands to yield complexes [[U(OSi(OtBu)3)2(crypt)]I, 3 and [[U(OSi(OtBu)3)2(18c6)]I, 4. Magnetic studies of these compounds offer a snapshot on how the SMM properties depend on the local symmetry in the presence of siloxide ligands. The static and dynamic magnetic properties of these compounds reveal a weak dependence of their single-molecule magnet behavior on the local symmetry.