Enantioselective aggregation and luminescence properties of europium(III) and terbium(III) complexes of an acetate and a tripodal ligand containing three imidazole groups

Abstract

The aggregation and luminescence properties of three pairs of EuIII (1–3) and isomorphous TbIII (4–6) complexes ligated to tripodal heptadentate N7 ligands and bidentate acetate ion, [EuIII or TbIII (H3L2-Me)(OAc)](ClO4)2·2MeOH·H2O (1,4), [EuIII or TbIII (H3L2-Me)(OAc)](ClO4)2·2EtOH (2,5), and [EuIII or TbIII(H3L5-Me)(OAc)](ClO4)2·MeOH (3,6), were studied, where H3L2-Me=tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine and H3L5-Me=tris[2-(((5-methylimidazol-4-yl)methylidene)amino)ethyl]amine, and OAc=acetate ion. Each EuIII or TbIII ion is coordinated by a heptadentate tripodal and a bidentate acetate ligand, resulting in Δ- and Λ-enantiomorphs because of the screw coordination arrangement of the tripodal ligand. Intermolecular imidazole⋯acetate hydrogen bonding gives rise to three types of enantioselective assemblies. Compounds 1 and 4 form homochiral 1D chains comprising an undulating double layer that crystallizes into a conglomerate, whereas 2 and 5 form homochiral, single-layer, 1D chains, and crystallize into a racemic crystal. 3 and 6 form heterochiral dimers possessing an inversion center. The solid-state emission spectra of the complexes display sharp bands corresponding to the f–f transitions. Quantum yields (Ф) of 0.21, 0.24, and 0.24 and lifetimes (τ) of 1.03, 0.98, and 0.97ms were obtained for the EuIII complexes 1, 2, and 3, respectively, under 310nm excitation. The corresponding values for the TbIII complexes 4, 5, and 6 were Ф=0.088, 0.10, and 0.043 and τ=0.46, 0.48, and 0.50ms, respectively.