The Inverse Trans Influence in a Family of Pentavalent Uranium Complexes

Systematic ligand variation in a structurally conserved framework of pentavalent uranium complexes of the formulas U^VX₂[N­(SiMe₃)₂]₃ (X = F, Cl, Br, N₃, NCS, 2-naphthoxide) and U^VOX­[N­(SiMe₃)₂]₃^– (X = −CCPh, −CN) allowed an investigation into the role of the inverse trans influence in pentavalent uranium complexes. The −CCPh and −CN derivatives were only stable in the presence of the trans-UO multiple bond, implicating the inverse trans influence in stabilizing these complexes. Spectroscopic, structural, and density functional theory calculated electronic structural data are explored. Near-IR data of all complexes is presented, displaying vibronic coupling of 5f¹ electronic transitions along the primary axis. Electrochemical characterization allowed assessment of the relative donating ability of the various axial ligands in this framework. Electron paramagnetic resonance data presented display axial spectra, with hyperfine coupling along the primary axis.