Stereocontrolled Self-assembly Of Lanthanide Coordination Supramolecular Cages

Chiral cage compounds are gaining increasing attention in coordination assemblies. Control of stereoselectivity is needed if chiroptical probes and sensors are to be developed. Through cooperative mechanical coupling effects, the chirality of the ligand can be transferred to either ? or ? metal stereochemistry during the self-assembly process. This phenomenon has recently been utilized for the preparation of enantiopure hosts, which enabled stereoselective guest recognition and/or reactions. Though self-assembly of chiral lanthanide coordination bundles and helicates has been recently demonstrated, stereocontrolled construction of lanthanide-containing cages has never been realized.We have succeeded in the stereoselective self-assembly of chiral luminescent europium coordination tetrahedral cages. The self-assembled cages are characterized by NMR, high-resolution ESI-TOF-MS, and in one case by X-ray crystallography. Strict control of stereoselectivity is confirmed by CD spectroscopy and NMR enantiomeric differentiation experiments. Narcissistic self-sorting is observed in the self-assembly process when two differently shaped ligands L₁ and L₂ are mixed. More impressively, distinct self-sorting behavior between Eu₄?L₁?₆ and Eu₄?L₂?₄ coordination cages is observed for the first time when racemic mixtures of ligands are used.Ligand is designed on the basis of the diarylethene for metal organic polyhedra building blocks. Corresponding chiral M₂L₃ topological polyhedra cage is assembled. Dramatic difference was observed for the photochromism process between the ligand and the M₂L₃ cage by using NMR, circular dichroism and mass spectrometry characterization methods...