Investigating the self-assembly and host-guest chemistry of inorganic polyhedral cages

Supramolecular cage complexes are of great interest, not only for their structural elegance, but also for their applications. Chapter 1 describes a collection of the many types of cage complexes based on three-dimensional polyhedral shapes and the host-guest chemistry that some cages complexes, enabled by their central cavities, are able to exhibit as they encapsulate small molecules.

This thesis contains a number of studies, starting with an investigation into the host-guest chemistry of the tetrahedral cage complex [M4(Lbip)6⊃(BF4)](BF4)7 [where M = Co(II) or Cd(II)]. Anion exchange is able to take place in these complexes, replacing tetrafluoroborate counterions for 1-naphthyl sulfonate or tetraphenylborate molecules. This is summarised in Chapter 2.

Chapter 3 details three experiments that look into the stability and the self-assembly process of tetrahedral cage complexes in solution. Two experiments involve the use of electrospray mass spectrometry, one to monitor the exchange of ligands between two tetrahedral cages, and the other to monitor the exchange of metal(II) ions between two isostructural cages. The third study follows the self-assembly of a tetrahedral cage by employing UV/vis spectroscopic titrations and uses equilibrium-restricted factor analysis to model the additive factors in the data as definite chemical species.

Chapters 4 and 6 describe new ligands and modifications to ligands by altering the pyrazolyl-pyridine binding units. It has been discovered that using pyrazine in place of pyridine (Chapter 4) on the ligands has a dramatic effect on the construction of the final product.

The encapsulation of neutral molecules by the cubic cage complex [Co8(L1,5-nap)12](BF4)16 is investigated in Chapter 5 and it has been discovered that coumarin binds to the internal cavity of the cage. The paramagnetic Co(II) metal centres cause the signals of the cage protons in the 1H NMR spectrum to be spread over a wide range (± 100 ppm). This makes it easy to see the guest signals and to identify any changes due to host-guest binding.