SELF-ASSEMBLY OF HELICAL SUPRAMOLECULAR LANTHANIDE COMPLEXES

The spontaneous strict self-assembly of tailored oligo-multidentate li gands with d-transition metal ions leads to the selective formation of polynuclear double- and triple-helical supramolecular complexes. A si gnificant improvement of the selectivity of the processes can be achie ved by using segmental ligands which possess different binding units c onnected by spacers favouring helical coordination and pure heteropoly nuclear helical complexes can be isolated under thermodynamic control. The application of these principles to 4f block ions requires the dev elopment of tridentate heterocyclic ligands designed for the synthesis of triple-helical self-assembled complexes containing lanthanides. Th e ligand 2,6 bis(1'-methyl-1H-benzimidazol-2'-yl)pyridine (L(4)) react s with Ln(3+) in acetonitrile to give the three successive complexes [ Ln(L(4))](3+), [Ln(L(4))(2)](3+) and [Ln(L(4))(3)](3+). The three liga nds in [Ln(L(4))(3)](3+) are wrapped around Eu(III) and produce a pseu do-D-3 symmetrical structure considered as a building block for triple -helical luminescent supramolecular structures. The introduction of tw o tridentate binding units into the oligomultidentate ligand L(6) lead s to the formation of dinuclear self-assembled triple-helical complexe s [Ln(2)(L(6))(3)](6+) which work as molecular light-converting device s on the nanometric scale. The photophysical properties together with the formation of analogous heterodinuclear and homotrinuclear complexe s are discussed.