Mono- and polymetallic lanthanide-containing functional assemblies: a field between tradition and novelty

Abstract

The variable and versatile co-ordination behaviour of lanthanide metal ions, Ln^III, limits their selective introduction into organised molecular or supramolecular architectures. The design of lanthanide-based devices is thus a special challenge since their specific electronic, magnetic or spectroscopic properties result from a precise control of the co-ordination sphere around the metal ions. The lock-and-key principle associated with the preorganisation of rigid macropolycylic multidentate ligands tailored for one particular Ln^III only partially fulfils these structural requirements. The development of less constrained macrocyclic ligands or macrocycles bearing pendant arms allows a smooth transition toward flexible (predisposed) receptors leading to the application of the induced fit principle in lanthanide co-ordination chemistry. According to this concept, programmed secondary non-covalent interstrand interactions (π-stacking, hydrogen bonds, electrostatic repulsion) assist the complexation process leading to an ultra-fine tuning of the metallic co-ordination sites. These two complementary approaches are discussed and evaluated for the design of organised mono-, di- and polymetallic lanthanide complexes together with the consideration of new semi-rigid multidentate podands which combine both aspects.