p-Carboxylatocalix[4]arenes : versatile building blocks for the assembly of novel nanostructures

Abstract

This thesis focuses on the synthesis and characterisation of supramolecular structures containing p-carboxylatocalix[4]arenes with pyridine derivative guest molecules. X-ray diffraction was predominantly utilised to help with the characterisation of these molecules. This thesis contains five chapters dealing with the synthesis and applications of novel p-carboxylatocalix[4]arenes. Chapter 1 gives a short overview of supramolecular chemistry, calixarene synthesis and their conformational properties. In addition, the supramolecular chemistry of several p-carboxylatocalix[4]arenes are also summarised. Chapter 2 describes the synthesis and characterisation of a variety of lower-rim di-functionalised p-carboxylatocalix[4]arenes. The lower-rim groups include alkyl, polyethylene glycol and alkenyl chains. With only one crystal structure generated containing a pyridine derivative, it is difficult to say if the other molecules synthesised will display the same behaviour. In the solid state this system was found to assemble via both the CO2H…CO2H homosynthon and the Py…CO2H heterosynthon and packed in a common bi-layer arrangement. Chapter 3 describes the effects of pyridine on the formation of a non-covalent assembly based on p-carboxyethylcalix[4]arene, which was found to pack in bi-layer arrays. Tetra-O-propoxy-p-carboxylatocalix[4]arene was synthesised in a different manner and was found to give a partial-cone conformation and when crystallised from DMF, gave a hydrogen-bonded head-to-head dimer through function of CO2H…CO2H interactions. Chapter 4 deals with calix[4]arenes fixed in a rigid cone conformation by selective lower-rim functionalisation. The effects of pyridine templates on the formation of non-covalent assemblies based on di-O-propoxy-di-p-carboxylatocalix[4]arene-crown-4 and p-carboxylatocalix[4]arene-biscrown-3 are described. These structures assemble via the Py…CO2H heterosynthon and the CO2H…CO2H homosynthon respectively. The latter compound was also used to form transition metal complexes/coordination polymers. Chapter 5 describes the effects of pyridine templates (including 2-AP) on the formation of non-covalent assemblies based on Suzuki cross-coupled tetra(p-benzoic acid)-tetrapropoxycalix[4]arene and di(p-benzoic acid)-tetrapropoxycalix[4]arene (and derivatives). The majority of these structures assemble via the Py…CO2H heterosynthon.