A hemiaminal-ether structure stabilized by lanthanide complexes with an imidazole-based Schiff base ligand

摘要

Imidazole-based lanthanide complexes bearing a hemiaminal-ether pendant, [Ln(L'-OR)(NO3)(2)] (NO3)center dot solvent (Ln = Tb and Gd; L'-OR = hemiaminal-ether ligand, 1,9-bis(1H-imidazole-4-yl)-5-[(R-1H-imidazole-4-yl) alkyl]-2,5,8-triazanon-1,8-dien; R = Me and Et; solvent = MeOH, EtOH, and H2O; abbreviated as LnL'-OR), were unexpectedly obtained from the reaction of diethylenetriamine with 4-imidazole-carbaldehyde in the presence of lanthanide nitrate in alcohol. These LnL'-OR structures were also obtained by treating dipodal imidazole-based lanthanide complexes [Ln(HL)(NO3)(2)(MeOH)](NO3)center dot MeOH (HL = bis{[2-{(imidazole-4-yl)methylidene} amino] ethyl} amine; abbreviated as LnHL) independently with (i) 4-imidazolecarbaldehyde, (ii) HNO3, or (iii) NO in alcohol. The results indicate that the hemiaminal-ether structure is stabilized by the lanthanide complex. The LnL'-OR structures were confirmed by X-ray analysis and cold electrospray ionization mass spectrometry in solution. The photophysical properties indicate that the L'-OR ligands can sensitize the Tb3+ luminescence. A significant spectral change was observed by the ligand component exchange. The exchange of the ligand component of the non-luminescent imidazole-based Tb complex, [Tb(MeL)(NO3)(2)](NO3) (MeL = bis{[2-{(1-methylimidazole-2-yl) methylidene} amino] ethyl} amine; abbreviated as TbMeL), results in a significant spectral change.