Controlling Self-assembly through Host-Guest Chemistry: Metallo-supramolecular Assemblies with Stellated Polyhedral Structures

Small molecules can be organised into large assemblies with distinct geometric shapes (especially polyhedral shapes such as cubes and octahedra) through the use of hydrogen bonding or metal-ligand coordination interactions. These assemblies are of interest to chemists because they are often nano-sized and highly complicated but, given the right conditions, effectively make themselves in a process called self-assembly. They often show internal space where other molecules can be trapped or even react, acting like nano-sized reaction vessels. Chemistry performed inside such confined spaces may produce results quite different to those found in bulk solutions.We propose to use ligands that have a rigid pyramidal shape to produce very large metal-ligand assemblies with polyhedral structures that have a stellated aspect. Stellations of a polyhedron look like spikes or pyramids emanating from the faces. We are looking to make assemblies with structures resembling stella octangula and stellated small cubicuboctahedron amongst others. These are dubbed the starburst prisms. While these types of structures are known mathematically there are very few examples of them in chemistry. The ligands we will use are known to be molecular hosts which mean that they can recognise or bind other molecules - in particular they have a great affinity with fullerenes. Hence we may be able to trap fullerenes or other guest molecules inside the stellation of these metal-ligand assemblies. The host-guest chemistry of the ligands can be used to control or manipulate the overall self-assembly. Discrete stellated assemblies will have the ligand binding sites all pointing inwards with particular geometric relationships between the binding sites. Hence templating guests with complementary geometries and sizes, or simply small guests will favour particular discrete stellated assemblies. Guest molecules that are not complementary for discrete structures due to their size or positioning of functional groups will instead favour polymeric metal-ligand materials, known as coordination polymers.These stellated assemblies (and any coordination polymers) will be studied by solid state (e.g. X-ray crystallography, thermal techniques) and solution techniques (e.g. mass spectrometry, DOSY NMR). the host-guest behaviour of the assemblies will be studied with a view to developing future applications of the assemblies as nano-sized reaction vessels, in catalysis, in molecular separations, and other fields.