Anchoring flexible uranyl dicarboxylate chains through stacking interactions of ancillary ligands on chiral UIJVI) centres †
Résumé
Reactions of aliphatic [small alpha],[small omega]-dicarboxylic acids HOOC-(CH2)n-2-COOH (H2Cn, with n = 6-9 and 13) with uranyl nitrate under solvo-hydrothermal conditions in the presence of N-donor chelators, either 2,2[prime or minute]-bipyridine (bipy) or 1,10-phenanthroline (phen), result in the crystallization of one-dimensional coordination polymers with the uranyl ions chelated by two carboxylate groups and the N-donor species. The eight complexes obtained, [UO2(C6)(bipy)][middle dot]H2O (1), [UO2(C7)(phen)] (2), [UO2(C8)(bipy)] (3), [UO2(C9)(phen)] (4 and 5), [(UO2)2(C9)(O2)(phen)2][middle dot]H2O (6), [UO2(C13)(bipy)] (7) and [UO2(C13)(phen)] (8) crystallize in two different arrangements, with the aza-aromatic ligands either alternating on opposite sides of the chains (1, 3, and 5-8) or located in a row on one side (2 and 4); the chains in complex 3 are peculiar in the series in that they assume a helical shape. In all cases, the tilting of the N-donor out of the uranyl equatorial plane induces chirality at the metal centre, and the chains are either homo- or heterochiral. Stacking interactions between aza-aromatic ligands, predominantly but with one exception bonded to uranium centres of opposite chirality, provide anchoring points for the otherwise flexible and weakly interacting chains. Emission from the solid complexes varies significantly in intensity but shows the well-known vibronic progression of the uranyl centre except for the peroxo species 6, where the emission appears to be ligand-centered.