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

Imidazole-based lanthanide complexes bearing a hemiaminal-ether pendant, [ Ln ( L ′-O R )(NO 3 ) 2 ](NO 3 )·solvent ( Ln = Tb and Gd; L′ -O R = hemiaminal-ether ligand, 1,9-bis(1 H -imidazole-4-yl)-5-[( R -1 H -imidazole-4-yl)alkyl]-2,5,8-triazanon-1,8-dien; R = Me and Et; solvent = MeOH, EtOH, and H 2 O; abbreviated as Ln L′ -O R ), were unexpectedly obtained from the reaction of diethylenetriamine with 4-imidazolecarbaldehyde in the presence of lanthanide nitrate in alcohol. These Ln L′ -O R structures were also obtained by treating dipodal imidazole-based lanthanide complexes [ Ln (H L )(NO 3 ) 2 (MeOH)](NO 3 )·MeOH (H L = bis{[2-{(imidazole-4-yl)methylidene}amino]ethyl}amine; abbreviated as Ln H L ) independently with (i) 4-imidazolecarbaldehyde, (ii) HNO 3 , or (iii) NO in alcohol. The results indicate that the hemiaminal-ether structure is stabilized by the lanthanide complex. The Ln L′ -O R structures were confirmed by X-ray analysis and cold electrospray ionization mass spectrometry in solution. The photophysical properties indicate that the L′ -O R ligands can sensitize the Tb 3+ 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(Me L )(NO 3 ) 2 ](NO 3 ) (Me L = bis{[2-{(1-methylimidazole-2-yl)methylidene}amino]ethyl}amine; abbreviated as TbMe L ), results in a significant spectral change. A hemiaminal-ether can be formed via four synthetic routes in alcohols using lanthanide complexes. The hemiaminal-ether structure is stabilized by the lanthanide complex.