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 CDCl(3), [D(4)]MeOH or [D(6)]DMSO and can be well characterised by (1)H 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.

An enantiomerically pure siderophore type ligand for the diastereoselective 1 : 1 complexation of lanthanide(III) ions.

A facile synthesis of a highly preorganized tripodal enterobactine-type ligand 1a-H3 consisting of a chiral C3-symmetric macrocyclic peptide and three tridentate 2-amido-8-hydroxyquinoline coordinating units is presented. Complex formation with various metal ions (Al(³+), Ga(³+), Fe(³+), La(³+) and Eu(³+)) was investigated by spectrophotometric methods. Only in the case of La(³+) and Eu(³+) were well defined 1 : 1 complexes formed. On the basis of CD spectroscopy and DFT calculations the configuration at the metal centre of the La(³+) complex was determined to show Lambda helicity. The coordination compounds [(1a)Ln] presented should be prototypes for further lanthanide(III) complexes with an enterobactine analogue binding situation.

Enhancement of near-IR emission by bromine substitution in lanthanide complexes with 2-carboxamide-8-hydroxyquinoline.

Three novel 2-carboxamide-8-hydroxyquinoline derivatives wrap helically around trivalent lanthanide ions to form monometallic 3 : 1 complexes possessing strong NIR emission.

2-[(8-Hydroxyquinolinyl)methylene]hydrazinecarboxamide: expanding the coordination sphere of 8-hydroxyquinoline for coordination of rare-earth metal(III) ions.

The semicarbazone of 8-hydroxyquinoline-2-carbaldehyde can be easily synthesized and is an effective tetradentate ligand for the coordination of rare-earth(III) ions. Investigations with yttrium(III) and lanthanum(III) in solution and in the solid state show, that the small yttrium ion can form 2 : 2 (1 : 1 stoichiometry) and 2 : 1 ligand to metal complexes (X-ray structures: [LY(NO3)(DMF)2]2Cl2 x 2DMF and [LL'Y] x 3MeOH x Et2O). With the larger lanthanum(III) ion only a well defined 1 : 1 complex (X-ray structure: [LLa(NO3)(MeOH)2]2(NO3)2) can be observed but probably 2 : 1 complexes are also formed. The X-ray structure analyses of [(L-H)MCl3] x MeOH (M = Er, Ho) and Na[(micro-NO3){LEu(NO3)2}2] x 2DMF show different coordination modes of the ligand. It can coordinate in its deprotonated but also in the protonated form.