Synthesis of uranium complexes incorporating extended azo-imine ligands: Molecular and electronic structure

The new azo-imine ligands 2,4-di-tert-butyl-6-((2-((2-hydroxyphenyl)diazenyl) phenylimino)methyl)phenol, H2L1, 1a, and 2,4-di-tert-butyl-6-((2-((2-hydroxyphenyl) diazenyl)p-chlorophenylimino)phenol, H2L2, 1b, were prepared. Reaction of H2L1; 1a, and H2L2; 1b, with uranyl nitrate hexahydrate afforded the mononuclear complexes of compositions [U(O)(2)(L-1)(H2O)]; 2a, and [U(O)(2)(L-2)(H2O)]; 2b, complexes respectively. The newly synthesised ligands (la and 1b) and the complexes (2a and 2b) were characterised unequivocally. The x-ray structure of 2a was determined. The tetradentate dianionic ligand (L-1)(2-) coordinated the uranium ion equatorially with a water molecule in the same plane. Two axially coordinated oxo ligands completed the overall pentagonal bipyramid geometry around U(VI) ion. Structural pattern, electron transfer properties (oxidation near 1.32 V vs Ag/AgCl) and electronic transitions of [U(O)(2)(L-1)(H2O)1; 2a, and [U(O)(2)(L-2)(H2O)]; 2b have been rationalized by DFT calculations.