Homo- and Heterodinuclear Helicates of Lanthanide(III), Zinc(II) and Aluminium(III) Based on 8-Hydroxyquinoline Ligands

Homonuclear helicates with rare-earth-metal(III) ions or heteronuclear derivatives with rare-earth-metal and aluminium or zinc centres are obtained in alkali-metal-templated self-assembly processes from isobutenylidene-bridged homoditopic bis(2-carbamido-8-hydroxyquinoline)-derived ligands 1-H-2 and 2-H-2 or heteroditopic (8-hydroxyquinoline)(2-carbamido-8-hydroxyquinoline)-derived ligands 3-H-2 and 4-H-2. Diamagnetic coordination compounds possess a high stability in organic solvents such as CDCl3, [D-4]MeOH or [D-6]DMSO and can be well characterised by H-1 NMR spectroscopy by using methylene protons and the protons of the vinylic units of the ligand as stereochemical or symmetry probes, respectively. Some of the homonuclear complexes could be crystallised and were characterised by using X-ray diffraction studies. The complexes adopt a triple-stranded helical structure with a central templating cation encapsulated in their interior. An unusual orientation of the double bond of one spacer towards this cation is observed. The homo- and heterodinuclear helicates with ytterbium(III), neodymium(III) or erbium(III) of ligands 2 and 4 were of special interest owing to their near-infrared (NIR) emitting properties, which were investigated depending on the lanthanide and on the encapsulated alkali-metal cation.