Ionic Radius Dependent Kinetic Behavior for the Self-Assemblyand Chiral Amplification of Lanthanide Tetrahedral Cages

Understanding the kinetic process during the self-assembly and chiral amplification of metal-organic polyhedra (MOPs) is critical for the rational preparation of chiral MOPs. Herein, we report the ionic radius dependent kinetic processes for the self-assembly and chiral amplification of Ln(4)L(4)-type (Ln, Lanthanides; L, ligand) lanthanide tetrahedral cages. The chiral Eu-4(L-R)(4) tetrahedral cage is structurally characterized by nuclear magnetic resonance (NMR), electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS), and single crystal X-ray diffraction. Kinetic study on the stereo-controlled self-assembly of circularly polarized luminescence (CPL)-active Ln(4)(L-R)(4) (Ln = La-III, Pr-III and Eu-III) tetrahedra manifests that the larger ionic radius of Ln leads to faster assembly rates. Mixed-ligand cage assembly experiments with chiral L-R/S, achiral L-ac and Ln (1 : 3 : 4 molar ratio) reveal that the self-assembly and chiral amplification occur synchronously for the La-III and Pr-III cages, while two distinct steps, i.e., first self-assembly and then chiral amplification, are observed for the Eu-III cage. Such distinct kinetic behavior is attributed to different ligands exchange rates among the mixed-ligand Ln(4)L(4) cages. This work provides fundamental guidance for fabrication and property-optimization of chiral lanthanide-based molecular materials.