[UIII{N(SiMe2tBu)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(SiMe3)(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.