Encapsulated Guests in the Smallest Spaces: Shrinking Guests by Compression and Investigations under Solvent-Free Conditions.

Noncovalent interactions play a pivotal role in a variety of biological and chemical processes. The experimental determination and quantum chemical calculations of the forces driving these interactions are of utmost importance. Of special interest are interactions of molecules in small spaces which show phenomena different from conventional behavior in solution. An extension is the encapsulation of guests in smallest spaces: The guests are too large to be included under standard conditions and hence must be forced to intrude into the cavity. Here, we show the design of such a host-guest system which allows to directly compare the measured thermodynamic values to gas-phase quantum chemical calculations. Structural investigation of the complexes reveals that the encapsulation process causes not only an extension of the hollow space of the host but also a shrinking of the included guest by compression.