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Only stable in the dark: when mixed with a metastable-state photoacid, metallasupramolecular structures become light sensitive. The photo-induced disassembly of the structures is reversed when the light is switched off., 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 liberating guest molecules with light.

The work presented in this thesis focused on the synthesis and characterization of new metalloligands based on iron(II) clathrochelate complexes. Clathrochelates can be functionalized peripherally with donor groups capable of coordinating metal ions. The synthetic accessibility of clathrochelate complexes, along with their excellent stability, and the broad structural and functional modifications possible, make this class of compound suitable to be used as building blocks in supramolecular chemistry. In chapter 1, a general introduction on supramolecular chemistry will be given. The chapter is focussing on the different approaches towards the process of self-assembly, and in particular on the use and properties of metalloligands. In chapter 2, clathrochelate complexes with terminal 3-pyridyl capping group are presented. These complexes were prepared by one-pot syntheses from commercially available or readily accessible starting materials. The resulting metalloligands were then incorporated in supramolecular coordination cages. Moreover, the influence of subtle changes in the structure of the ligands, and in particular in the aspect ratio of the ligands, was investigated as decisive factors which drive self-assembly processes towards different assemblies. In chapter 3, tetratopic clathrochelate-based metalloligands with appended 4-pyridyl functions are presented. These complexes were obtained by high-yield coupling reactions of brominated clathrochelate complexes. The metalloligands were used for the construction of novel supramolecular cages with gyrobifastigium geometry. The unusual geometry that arises from the combination of the new metalloligands and cis-blocked PtII and PdII complexes was explained on the base of steric interactions. In chapter 4, three novel tetratopic ligands with an extended range of aspect ratios are discussed. The ligands were tested in combination with cis-blocked PtII complexes. The results of these experiments confirmed that in the rational design of supramolecular assemblies, there is still ample room for surprises. The influence of the aspect ratio of ligands is not to be underestimated, and structurally very different assemblies were characterised. The characterization includes X-ray single crystal analyses. Thanks to the latter, we were able to confirm the formation of a sizable M8L16 molecular square orthobicupola, that is one of the biggest discrete assemblies reported to date. In order to give new functions to molecular cages based on clathrochelates, we move a first step towards the synthesis of redox-active molecular cages. This work is presented in chapter 5. The library of tetratopic ligands in our hands was enlarged with the synthesis of new iron(II) clathrochelate complexes based on redox non-innocent dioximes. The syntheses and characterisations of these new compounds and their precursors are reported. A preliminary electrochemical study of the ligands is also described. The ligands were then used for the synthesis of new supramolecular cages. The assemblies did not show reversible redox events. Nevertheless, the structural characterization can serve as a starting point to further investigations. In chapter 6, the syntheses of new metalloligands are discussed along with their precursors. An extensive characterization of the new complexes is given. Some of the building blocks were tested in combination with metal complexes or salts to investigate their behaviour as supramolecular subunits.

It is possible to control the geometry and the composition of metallasupramolecular assemblies via the aspect ratio of their ligands. This point is demonstrated for a series of iron- and palladium-based coordination cages. Functionalized clathrochelate complexes with variable aspect ratios were used as rod-like metalloligands. A cubic FeII8L12 cage was 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. In a related fashion, it was possible to control the geometry of PdII-based coordination cages. A metalloligand with a large aspect ratio gave an entropically favored tetrahedral PdII4L8 assembly, whereas an octahedral PdII6L12 cage was formed with a ligand of the same length but with an increased width. The aspect ratio can also be used to control the composition of dynamic mixtures of PdII cages. Out of two metalloligands with only marginally different aspect ratios, one gave rise to a self-sorted collection of PdII4L8 and PdII6L12 cages, whereas the other did not.

Large (Mw > 10 kDa) heterometallic coordination cages with gyrobifastigium-like geometry are obtained by using metalloligands with sterically demanding FeII clathrochelate cores and four divergent pyridyl groups. Upon reaction with cis-blocked PtII and PdII complexes, MII8L4 cages are formed. The gyrobifastigium geometry of these cages is in contrast to the barrel-like structures which are typically observed for metallasupramolecular assemblies with M8L4 stoichiometry.