Helicate-to-tetrahedron transformation of chiral lanthanide supramolecular complexes induced by ionic radii effect and linker length

Controlled formation of desired lanthanide supramolecular complexes is challenging because of the difficulties in predicting coordination geometry, as well as a labile coordination number. Herein, we explore the effect of ionic radii and linker length on supramolecular species formation. A helicate-to-tetrahedron transformation occurred between [Ln(2)L1(3)] and [Ln(4)L1(6)] (Ln = La, Sm, Eu, Gd, Tb and Lu). For six lanthanide ions, the unfavored tetrahedron [La(4)L1(6)] can only be observed in a concentrated mixture with the helicate [La(2)L1(3)] where no pure [La(4)L1(6)] species was isolated via crystallization. For Sm, Eu, Gd, Tb, the [Ln(4)L1(6)] supramolecular tetrahedron can be isolated via crystallization from diisopropyl ether. A similar result was also observed for Lu, but the tetrahedral structure was found to be relatively stable and transformed back to [Lu(2)L1(3)] much slower upon dissolution. No tetrahedron formation was observed with L3 giving rise to only [Ln(2)L3(3)] species, in which L3 contains a longer and more flexible linker compared with that of L1. Results show that the supramolecular transformation in these systems is governed by both the ionic radii as well as the ligand design. Special focus is on both [Eu(2)L1(3)] and [Eu(4)L1(6)] which form chiral entities and exhibit interesting circular polarized luminescence. Lanthanide-based supramolecular complexes have labile and hard-topredict chemical structures. Here the authors show controlled formation of either helicates or tetrahedron shaped cages based on the interplay between the metal ionic radius and the ligand composition.

Automated summary

The study investigates the impact of ionic radii and linker length on the formation of lanthanide supramolecular complexes, revealing that the supramolecular transformation is governed by both the ionic radii as well as the ligand design. Controlled formation of helicates or tetrahedron shaped cages is achieved by adjusting the interplay between the metal ionic radius and the ligand composition.