Molecular nanostructures based on polyfunctional clathrochelate complexes

This thesis describes the design and synthesis of clathrochelate metalloligands for the construction of molecular nanostructures. The low synthetic effort, versatility and stability of the clathrochelate metalloligands makes them particularly suited to the construction of coordination structures. Chapter 2 shows it is possible to control the geometry and the composition of metallasupramolecular assemblies via the aspect ratio of their ligands. Functionalized clathrochelate complexes with variable aspect ratios were used as rod-like metalloligands. Cubic FeII8L12 cages were obtained from a metalloligand with an intermediate aspect ratio. By increasing the length or by decreasing the width of the ligand, the self-assembly process resulted in the clean formation of tetrahedral FeII4L6 cages instead of cubic cages. Chapter 3 describes a simple one-step protocol, which allows large bipyridyl functionalized double clathrochelate metalloligands with an overall bent shape to be synthesized from easily accessible and/or commercially available starting materials. The ligands were used to construct PdII2L4-type coordination cages of unprecedented size. Furthermore, evidence is provided that these cages may be stabilized by close intramolecular packing of lipophilic ligand side chains. In Chapter 4, even larger triple clathrochelate metalloligands were used to form two PdII6L8-type coordination cages. With molecular weights of more than 15 kDa and Pd···Pd distances of up to 4.2 nm, these complexes are among the largest palladium cages described to date. In the 5th chapter, the stability of five different [Pdn(N donor)m]2n+ assemblies was examined by performing disassembly experiments with pyridine and with trifluoroacetic acid. Pyridine-induced disassembly was found to be most pronounced for Pd complexes containing N-donor ligands of low basicity. At the same time, these assemblies displayed high acid resistance. The contrasting stability in the presence of acid or pyridine can be used for the pH-controlled switching between different metallosupramolecular structures. The final research section (Chapter 6) shows that the addition of a metastable-state photoacid to solutions containing metal-ligand assemblies renders the systems light responsive. Upon irradiation, proton transfer from the photoacid to the ligand is observed, resulting in disassembly of the metallasupramolecular structure. In the dark, the process is fully reversed. Light-induced switching was demonstrated for six different metal ligand assemblies containing PdII, PtII or RuII complexes and bridging polypyridyl ligands. The methodology allows the liberation of guest molecules using light as a stimulus.

Severin, Kay
Lausanne, EPFL

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