Triply bridged binuclear lanthanides-Zwitterion complexes: synthesis and characterization of (Gd(III), Nd(III), Sm(III)) complexes

Abstract

2,2'-((1E,1'E)-(Butane-1,4-diylbis (azanylylidene))bis (methanylylidene)) diphenol zwitterion (L) (4′) was prepared by treatment of two equiv. of (3-(2-furyl)acrolein) (1) with one equiv. of 1,4-butanediamine (2) in refluxing ethanol through an intramolecular Diels-Alder reaction. Three new lanthanide compounds based on (4′), [Ln2(NO3)4(H2O)2L3]·2NO3 (5) (a, Ln = Gd; b, Ln = Nd; c, Ln = Sm), have been obtained and further characterized by elemental analysis, conductivity, magnetic measurements, FT-IR, powder X-ray and thermogravimetric analysis. Compounds 5a–c exhibit a discrete dinuclear structure constructed by three ligands coordinating two Ln3+ ions. The oxygen atoms of the diphenol are involved in the coordination of 5, while the nitrogen atoms of the imines are not involved. Hypersensitive transitions could be observed at 877, 807, 753, 588, and 522 nm in the UV–visible absorption spectrum of the neodymium complex 5 b, corresponding to 4I9/2→4F3/2 (877 nm); 4I9/2→4F5/2, 2H9/2 (807 nm); 4I9/2→4S3/2, 4F7/2 (753 nm); 4I9/2→2G7/2, 4G5/2 (588 nm); 4I9/2→4G9/2 4G7/2, and 2K13/2 (522 nm), respectively. Emission spectra of the ligand and its samarium complex 5c revealed characteristic luminescence within the visible region with the emission of the samarium complex being relatively red shifted.