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

Abstract

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.

Acridone‐Benzimidazole Ring‐Fused Ligands: A New Class of Sensitizers of Lanthanide Luminescence via Low‐Energy Excitation

“…the absorbing d-block and the emissive lanthanide ion, that often reduces the efficiency of the energy transfer. Finally, it is also feasible to funnel energy through visible absorption bands (π-π* or intra-ligand charge transfer, ILCT) of purely organic chromophores such as fluorescein, [18] rhodamine, [19] 8-hydroxyquinoline, [20][21][22] carbazole- [4] or tetrazine-based [23] ligands, as well as boradiazaindacene dyes, [24] to name but a few examples. However, visible-absorbing organic chromophores with do- 3 [25] polyaminocarboxylates with one pendant arm bearing a sensitizing acridone group, [26,27] [Eu(fod) 3 (MK)] complex (MK = Michler's ketone, fod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-dione), [28] and [Eu(PHN) 3 (H 2 O)(DMF)]-PHN (HPHN = 9-hydroxyphenal-1-one), [29] only the ternary complex prepared by Zhang's group [25] displays remarkable photophysical properties; the overall quantum yield amounts to 52 % in toluene, this sizeable value being due to efficient energy transfer which, unusually, operates from a singlet state.…”

Hydroxyquinoline–Calix[4]arene Conjugates as Ligands for Polynuclear Lanthanide Complexes: Preparation, Characterization, and Properties of a Dinuclear EuIII Complex

“…The 8‐hydroxyquinoline ligand (HOQ) is one of the most popular gravimetric reagents for trivalent metal ions because of the low solubility of the resulting complexes . 8‐Hydroxyquinolinolato complexes of the rare earth elements have also been studied as extraction agents, infrared‐emitting molecular materials, and as therapeutic agents for metal chelation, while some derivatives of 8‐hydroxyquinoline were employed in the construction of self‐assembled lanthanide helicates and heterobimetallic lanthanide/alkaline earth metal complexes . However, only a few rare earth quinolinolato complexes have been obtained as single crystals suitable for X‐ray diffraction analysis due to their low solubility.…”

Homodinuclear f–f and Heterodinuclear f–p Lanthanide Helicates

“…The process described for [( 14c ) 3 AlYbK]OTf is also found for the corresponding erbium(III) and neodymium(III) complexes. Interestingly the observation of the red ligand emission is strongly dependent on the templating cation and can be dramatically reduced by using larger cations like rubidium or caesium 19.…”