Ditopic 8-Hydroxyquinoline-2-carboxamides as Ligands for the Formation of Dinuclear Lanthanide(III) Helicates

Coordination-Directed Self-Assembly of Functional Polynuclear Lanthanide Supramolecular Architectures

Lanthanide supramolecular chemistry is a fast growing and intriguing research field due to the unique photophysical, magnetic, and coordination properties of lanthanide ions (Ln^III). Compared with the intensively investigated mononuclear Ln-complexes, polymetallic lanthanide supramolecular assemblies offer more structural superiority and functional advantages. In recent decades, significant progress has been made in polynuclear lanthanide supramolecules, varying from structural evolution to luminescent and magnetic functional materials. This review summarizes the design principles in ligand-induced coordination-driven self-assembly of polynuclear Ln-structures and intends to offer guidance for the construction of more elegant Ln-based architectures and optimization of their functional performances. Design principles concerning the water solubility and chirality of the lanthanide-organic assemblies that are vital in extending their applications are emphasized. The strategies for improving the luminescent properties and the applications in up-conversion, host-guest chemistry, luminescent sensing, and catalysis have been summarized. Magnetic materials based on supramolecular assembled lanthanide architectures are given in an individual section and are classified based on their structural features. Challenges remaining and perspective directions in this field are also briefly discussed.

Lanthanide-directed synthesis of luminescent self-assembly supramolecular structures and mechanically bonded systems from acyclic coordinating organic ligands

Herein some examples of the use of lanthanide ions (f-metal ions) to direct the synthesis of luminescent self-assembly systems (architectures) will be discussed. This area of lanthanide supramolecular chemistry is fast growing, thanks to the unique physical (magnetic and luminescent) and coordination properties of the lanthanides, which are often transferred to the resulting supermolecule. The emphasis herein will be on systems that are luminescent, and hence, generated by using either visibly emitting ions (such as Eu(III), Tb(III) and Sm(III)) or near infrared emitting ions (like Nd(III), Yb(III) and Er(III)), formed through the use of templating chemistry, by employing structurally simple ligands, possessing oxygen and nitrogen coordinating moieties. As the lanthanides have high coordination requirements, their use often allows for the formation of coordination compounds and supramolecular systems such as bundles, grids, helicates and interlocked molecules that are not synthetically accessible through the use of other commonly used templating ions such as transition metal ions. Hence, the use of the rare-earth metal ions can lead to the formation of unique and stable species in both solution and in the solid state, as well as functional and responsive structures.

Recent Highlights in the use of Lanthanide-directed Synthesis of Novel Supramolecular (Luminescent) Self-assembly Structures such as Coordination Bundles, Helicates and Sensors

In this short review, we focus on the recent developments within the field of coordination chemistry where mono- or multimetallic supramolecular self-assemblies are formed by employing structurally defined organic ligands, taking advantage of the high coordination requirements of the lanthanides. Such synthesis results in the formation of both structurally complex and beautiful self-assemblies. Moreover, as the lanthanide ions possess both unique magnetic (e.g. GdIII and DyIII) and luminescent properties, either in the visible (EuIII, SmIII and TbIII) or near-infrared regions (YbIII, NdIII, ErIII), these physical features are usually transferred to the self-assemblies themselves, allowing the formation of highly functional structures, such as coordination networks, as well as molecular bundles and helicates. Hence, examples of the use of lanthanide-directed synthesis of luminescent sensors, some of which are formed on solid surfaces such as gold (flat surface or nanoparticles), and imaging agents are presented. Moreover, we demonstrate that by using chiral organic ligands, lanthanide-directed synthesis can also give rise to the formation of enantiomerically pure self-assemblies, the structure of which can be probed using circularly polarized luminescence.