Separation of actinides and lanthanides:: crystal and molecular structures of N,N′-bis(3,5-di-t-butylsalicylidene)-4,5-dimethyl-1, 2-phenylenediamine and its uranium complex

The preparation of the tetradentate dianionic ligand N,N'-bis(3,5-di-t-butylsalicylidene)-4,5-dimethyl-1,2-phenylenediamine [H2L] is described, together with the corresponding uranium complex [UO2(L)CH3OH]. H2L has been found to selectively bind to a representative actinide (UO22+) rather than to lanthanum (La3+) due to its cavity size. Both the free ligand and uranyl complex were characterized by elemental analysis, spectroscopic methods and single-crystal X-ray diffraction. The crystal structure of [UO2(L)CH3OH] complex show that uranyl cation adopts a distorted pentagonal bipyramidal conformation, with two imine nitrogen atoms, two phenolic oxygen atoms and a methanol oxygen in the coordination sphere, together with two trans oxo groups. The oxo groups have a (O-U-O, 176.85(15)degrees) angle consistent with linear coordination and U-O bond lengths of 1.786(4) and 1.805(4)Angstrom. The difference in the bond distances can be ascribed to the existence of a hydrogen bond between one uranyl oxygen and the O-H of a methanol of neighboring molecule. This complex has one of the highest solubilities in organic solvents of all uranium compounds, making it a potential candidate for applications in solvent extraction. (C) 2004 Elsevier Ltd. All rights reserved.