Mono- and dinuclear uranyl(VI) complexes with chiral Schiff base ligand

Slow evaporation of an equimolar solution containing chiral uranyl-salen-pyrene complex and (L)-phenylalanine tetramethylammonium salt ((L)-Phe-TMA) in toluene/EtOH mixture produced crystals built by anionic mononuclear [(UO2)(L)(L′)]- and dinuclear [(UO 2)2(L)2(μ2-OH)]- (L = salen-pyrene, L′ = pyrenolate) complexes, counterbalanced by tetramethylammonium (TMA) cations. The single-crystal X-ray diffraction analysis shows that in both complexes the salen-pyrene ligand acts as a tetradentate ligand through its nitrogen and oxygen atoms chelating the UO2 2+ ion at the equatorial plane. Uranium centers show a seven-coordinated pentagonal-bipyramidal environment, where the fifth equatorial site is occupied by an oxygen atom from the pyrenolate ligand in the monomer and a μ2-OH bridging group in the dimer. In the dinuclear complex the central μ2-OH bridges two UO2 2+ ions forming a double-stranded helical structure. TMA cations are sandwiched between the anionic uranyl-salen-pyrene complexes through weak hydrogen bonds and cation⋯π interactions. This produces alternating monomer/TMA/dimer/TMA pillars assembled by van der Waals interactions in the three-dimensional crystal lattice. The chiral uranyl-salen-pyrene receptor and the mixture of mono- and dimeric complexes have been also characterized by ESI-MS, UV-Vis and fluorescence spectroscopy. © 2012 Elsevier B.V. All rights reserved