Luminescent europium(III) complexes of tripodal heptadentate N 7 ligands containing three imidazole groups

Abstract

Luminescent Eu III complexes with tripodal heptadentate N 7 ligands containing three imidazole groups, [Eu III(H 3L 2-H)(ac)](ClO 4) 2·H 2O ( 1), [Eu III(H 3L 2-Me)(ac)](ClO 4) 2·2EtOH ( 2), and [Eu III(H 3L 4-Me)(ac)](ClO 4) 2·H 2O ( 3), were synthesized and characterized, where H 3L 2-H, H 3L 2-Me, and H 3L 4-Me are the tripodal ligands derived from the 1:3 condensation of tris(2-aminoethyl)amine and either 4-formylimidazole, 2-methyl-4-formylimidazole, and 4-methyl-5-formylimidazole, respectively, and ac denotes an acetate ion. Single-crystal X-ray analyses revealed that each Eu III ion is coordinated by a tripodal heptadentate N 7 ligand and two oxygen atoms of the acetate ion as a bidentate ligand. The complexes displayed sharp emission bands based on the f–f transitions by excitation at 261 nm in acetonitrile. The emission intensities increased in the order 1 < 2 < 3 in acetonitrile, while the emission spectra were quenched in aqueous solution due to the partial dissociation of the acetate ion and tripodal ligand.