Controlling Supramolecular Topology — The Art of Building Supermolecules

Abstract

In the previous chapter we introduced host-guest chemistry based on specific molecular interactions, which is the bedrock of supramolecular chemistry. It is worth noting at this point that complexation between appropriate hosts and guests can also be used to form large aggregates. However, before we dive into the subject of large assemblies in the next chapter, we are first going to investigate medium-size supermolecules. Various families of novel supermolecules obtained via spontaneous or designed covalent linkages have been attracting a great deal of attention recently. These supermolecules have interesting and unique geometric features and provide the key to many tailored supramolecular topologies, and it is these molecules that we explore in this chapter. Some examples include the following. Fullerenes are closed spheroid structures created from carbon pentagons and hexagons. Some of them can be described as "molecular soccer balls". Tubular structures-carbon nanotubes-can also be created by combining hexagons and pentagons of carbon. Systematic molecular branching and extension results in the stepwise formation of dendrimers, which can trap other molecules or ions. Threading rod molecules through rings (cyclic molecules) results in rotaxanes, and interlocking ring-like molecules together creates cate-nanes. Some of these molecules are obtained through spontaneous processes while the others are constructed via well-designed synthetic strategies.