Synthesis, Spectroscopy, and Theoretical Details of Uranyl Schiff-Base Coordination Complexes

Two uranyl Schiff-base coordination complexes, UO₂L(MeOH) and UO₂Cl₂(H₂L) {L = N,N′-bis[(4,4′-diethylamino)salicylidene]-1,2-phenylenediamine}, have been synthesized that feature a rigid phenyl backbone. These complexes have been characterized by structural, spectroscopic, and theoretical analysis to offer an electronic structure basis to explain the bonding parameters and stability. Single-crystal X-ray analysis reveals that UO₂L(MeOH) adopts the typical "soft taco confirmation" characteristic of uranyl salophen complexes, whereas UO₂Cl₂(H₂L) features an unusual neutral ligand coordination that contains an internal hydrogen bond between the phenol and imine. Rate constants calculated from electrochemical experiments confirm a quasi-reversible UO₂ ²⁺/UO₂ ⁺ couple. Single-configurational and multiconfigurational methods were used to explore the bonding in UO₂L(MeOH) and UO₂Cl₂(H₂L).