Diastereoselective formation of luminescent dinuclear lanthanide(iii) helicates with enantiomerically pure tartaric acid derived bis(β-diketonate) ligands

The chiral tartaric acid derived bis(β-diketonate) ligands 1–3-H₂ diastereoselectively form dinuclear triple-stranded helicates with a series of lanthanide(III) ions (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb), which bind water molecules as additional co-ligands. In the cases of europium(III) and terbium(III) ions, bright red or green luminescence is observed, respectively. Hereby the energy transfer from the ligand to the metal is most effective with the bromophenyl-substituted ligand 3-H₂. Reaction of 3-H₂ with europium(III) in a 4 : 2 ratio results in a highly luminescent quadruple-stranded dinuclear complex [3₄Eu₂]^2–.