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

Two uranyl Schiff-base coordination complexes, UO and UO {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 UO adopts the typical "soft taco confirmation" characteristic of uranyl salophen complexes, whereas UO 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 UO₂²⁺/UO₂⁺ couple. Single-configurational and multiconfigurational methods were used to explore the bonding in UO and UO. For UO, the U-Cl bond exhibits more covalent contributions than U-O_L.