Separation of actinides and lanthanides: Synthesis and molecular structure of a new di-mu-phenoxo-bridged dinuclear bis(dioxouranium(VI)) complex

The new phenoxo-bridged uranyl [(UO2)(2)L-2(thf)(2)] [H2L = N(2-oxyphenyl)-3-methoxy salicylaldiminato (C14H11NO3)] compound has been synthesized and characterized. The 3D structure of the free ligand is also reported. The complex crystallizes in the monoclinic space group P2(1)/c with lattice parameters a = 19.5915(15) angstrom, b = 10.4096(9) k, c = 17.5216(14) angstrom and beta = 99.9960(7)degrees with z = 4. The compound consists of a dinuclear unit composed of two dioxouranium(VI) ions, bridged by two phenoxide oxygens. The coordination around each uranium atom can be regarded as approximately pentagonal bipyramidal. The two uranyl groups are separated by 3.9192(5),. The title complex is one of the few examples for bis-uranyl groups bridged by phenoxo ligands. These types of ligands are candidates for the sequestration of the uranium from nuclear waste and provide a good selectivity over competing lanthanide cations in solution. The ligand has been found to selectively bind to a representative actinide (UO22+) rather than to lanthanum (Ln(3+)), which is probably related to the larger ionic radii of Ln(III). So, the ligand is not suitable to clutch two lanthanide metals via the phenolate bridge (Ln-O-(phenol)-Ln). The spherical shape and the larger size of the Ln(III) ions apparently do not allow a fit within the byte angle of phenolate bridge. (c) 2005 Elsevier B.V. All rights reserved.