Directed assembly of p-Carboxylatocalix[4]arenes

Abstract

The research in this thesis is centred on the design and development of novel coordination polymers (CPs) constructed from p-carboxylatocalix[4]arenes. Two design strategies were chosen as potential methods that would enable the rational design of CPs using transition metals (TMs) as directing centres and p-carboxylatocalix[4]arenes as building blocks. Each strategy was based on synthesising a target motif. The selection criteria for the target motifs were: 1) to provide the directionality in which the assembly could be extended and 2) be easily reproducible for a series of TMs. The first target motif is a planar binuclear metal cluster that can be extended in all three dimensions. The second motif is a TM complex containing a chelating ligand restricting the number of binding sites in the coordination sphere available to subsequent binding of ligands. In the preliminary study, using TM(II) ion (Co, Mn, Cd), mono-p-carboxylatocalix[4]arenes and bipyridines, a series of 1D CPs containing the target planar molecular panel were synthesised and characterised. The application of the "directional bonding" approach resulted in formation of the target second motif, a discrete coordination complexes constructed from TM(II) ion (Mn, Cd), mono-p-carboxylatocalix[4]arene and 1,10-phenanthroline. In the following study it was found that the steric effects of co-ligands used and the pre-organisation of the calixarene building block have a significant influence over the assembly process, dictating the topology of formed supramolecular architectures. Utilisation of the strategy based on the "directional bonding" approach, utilisation of a di-topic di-p-carboxylatocalix[4]arene resulted in formation of linear 1D CPs. Through exploitation of the di-O-alkoxycalix[4]arene C2 symmetry an alternative di-topic calixarenes were synthesised and used to construct spiral 1D CPs. It was also found that in certain reaction conditions these alternative di-p-carboxylatocalix[4]arenes assemble into discrete dimeric metal-organic calixarene capsules rather than spiral 1D CPs. In addition, it was demonstrated that di-p-carboxylatocalix[4]arene can also be used to synthesise 3D CPs.