[U(III) {N(SiMe2 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(SiMe2 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.