[U(III){N(SiMe(2)tBu)(2)}(3)]: A Structurally Authenticated Trigonal Planar Actinide Complex

We report the synthesis and characterization of the uranium(III) triamide complex [U(III)(N**)(3)] [1, N**=N(SiMe(2)tBu)(2)(−)]. Surprisingly, complex 1 exhibits a trigonal planar geometry in the solid state, which is unprecedented for three-coordinate actinide complexes that have exclusively adopted trigonal pyramidal geometries to date. The characterization data for [U(III)(N**)(3)] were compared with the prototypical trigonal pyramidal uranium(III) triamide complex [U(III)(N“)(3)] (N”=N(SiMe(3))(2)(−)), and taken together with theoretical calculations it was concluded that pyramidalization results in net stabilization for [U(III)(N“)(3)], but this can be overcome with very sterically demanding ligands, such as N**. The planarity of 1 leads to favorable magnetic dynamics, which may be considered in the future design of U(III) single-molecule magnets.