Luminescent europium(III) complexes of tripodal heptadentate N7 ligands containing three imidazole groups

Luminescent EuIII complexes with tripodal heptadentate N7 ligands containing three imidazole groups, [EuIII(H3L2-H)(ac)](ClO4)2·H2O (1), [EuIII(H3L2-Me)(ac)](ClO4)2·2EtOH (2), and [EuIII(H3L4-Me)(ac)](ClO4)2·H2O (3), were synthesized and characterized, where H3L2-H, H3L2-Me, and H3L4-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 EuIII ion is coordinated by a tripodal heptadentate N7 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.

Graphical abstractLuminescent europium(III) complexes with tripodal heptadentate N7 ligands containing three imidazole groups were synthesized and characterized. The single-crystal X-ray analyses revealed that EuIII ion is coordinated by a tripodal heptadentate N7 ligand and two oxygen atoms of acetate ion as a bidentate chelate ligand. The complexes display sharp emission bands based on the f–f transitions by excitation at 261 nm in 1.0 × 10−5 M acetonitrile solution, while the emission spectra were quenched in aqueous solution due to the partial dissociation of the ligand.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Luminescent EuIII complexes with tripodal ligands were synthesized and characterized. ► Ligands are 1:3 condensation of tris(2-aminoethyl)amine and 4-formylimidazoles. ► Each EuIII ion has a N7O2 coordination sphere of a tripodal ligand and acetate ion. ► The complexes displayed sharp emission bands based on the f–f transitions.