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

Abstract

The preparation of the tetradentate dianionic ligand N,N′-bis(3,5-di- t-butylsalicylidene)-4,5-dimethyl-1,2-phenylenediamine [H 2L] is described, together with the corresponding uranium complex [UO 2(L)CH 3OH]. H 2L has been found to selectively bind to a representative actinide ( UO 2 2 + ) rather than to lanthanum (La 3+) 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 [UO 2(L)CH 3OH] 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)°) angle consistent with linear coordination and U–O bond lengths of 1.786(4) and 1.805(4) Å. 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.