For decades, the chloric acids, the blue color of starch iodine mixture and the hydrate of chlorine gas were chemical oddities. Suddenly, following the accidental discovery of the crystalline urea complex of octyl alcohol by Bengen in 1940, there was a tremendous burst of activity and interest in these compounds by the oil companies. It was soon discovered that these complexes, referred to as Inclusion Compounds, have several valuable commercial and laboratory uses.
The inclusion compounds are of two general types, the cage or clathrates (Greek word meaning “lock” ) and the channel compounds.
These compounds have one underlying principle in common: their formation depends on the spatial “fitting in” of the guest molecules into the crystal lattice cavities or the “holes” of liquid aggregates of host molecules. There is on chemical affinity between the host and guest molecules in the usual sense, e.g., inclusion compounds of even the inert gases have been formed. Inclusion compound formation depends upon the size and the share of guest molecules and the reciprocal size of the cavities created by the host molecules.
This brings about a very close contact of the molecules, and the short-ranging van der Waals forces become significant factors for compound formation.