Supramolecular chemistry is regarded in its simplest sense as involving some kind of (noncovalent) binding or complexation event; we must immediately define what is doing the binding. In this context we generally consider a molecule (a host) binding another molecule (a guest) to produce a host-guest complex or supramolecule. Commonly the host is a large molecule or aggregate such as an enzyme or synthetic cyclic compound possessing a sizeable, central hole or cavity. The guest may be a monoatomic cation, a simple inorganic anion, or a neutral molecule. More formally, the host is defined as...