Self-assembly of 2-aldehyde-8-hydroxyquinolinate-based lanthanide complexes and NIR luminescence

• Five mononuclear lanthanide complexes were obtained.
• Two distinct ligands were in-situ self-assembled.
• Ce3+ ions were oxidized to Ce4+ ions in the reaction mixture.
• NIR luminescence of Yb3+ ions was observed.

Self-assembly reaction of 2-aldehyde-8-hydroxyquinoline, tris(hydroxymethyl)aminomethane and LnCl3⋅6H2O affords a series of mononuclear lanthanide complexes Ce(baho)2·Et2O (1) (H2baho = 2,8-bis(2-(8-hydroxylquinolinyl))-1-aza-5-hydroxymethyl-3,7-dioxabicyclo[3.3.0]octane), Dy(nhm)2Cl·0.5H2O (2) and Ln(nhm)2Cl·0.5C6H14 (Ln = Ho (3), Er (4), Yb (5) and Hnhm = N-(2-(8-hydroxylquinolinyl)methylene)(trishydroxymethyl)methylamine. The crystal structures have been determined by X-ray crystallographic analysis, and the tetravalence of Ce in 1 has been proven by XPS. Interestingly, the positive charge of Ce4+ ion in 1 is neutralized by two deprotonated baho2− ligands, while two deprotonated nhm− ligands and one Cl− compensate the positive charge of Ln3+ ions in 2–5. Complex 5 exhibit essential NIR luminescence of Yb3+ ion with lifetime of 17.64 μs in solid and 9.96 μs in CH3OH solution.

A series of mononuclear lanthanide complexes were isolated and characterized. Cerium was found in tetravalence with an unexpected ligand 2,8-bis(2-(8-hydroxylquinolinyl))-1-aza-5-hydroxymethyl-3,7-dioxabicyclo[3.3.0]octane in 1, in contrast to Ln3+ ions (Ln = Dy (2), Ho (3), Er (4) and Yb (5)) with a Schiff-base ligand. The NIR luminescent behavior of 5 was further investigated.Figure optionsDownload as PowerPoint slide