A<unk>  or<unk>  or cage<unk>  is a chemical substance consisting of a lattice of one type of molecule trapping and containing a second type of molecule. The word<unk>  is derived from the  Latin clatratus meaning with bars or a lattice. An example of a<unk>  is<unk>  hydrate, a special type of gas hydrate in which a lattice of water molecules encloses molecules of a trapped gas. Scientists believe that<unk> s on the sea bed have trapped large amounts of methane in similar configurations.  Researchers have begun to investigate silicon and germanium<unk> s for possible semiconducting and superconducting properties.
A<unk>  therefore is a material which is a weak composite, with molecules of suitable size captured in spaces which are left by the other<unk> s. They are also called host-guest complexes, inclusion<unk> s, and adducts (chiefly in the case of urea and thiourea).  They used to be called "molecular<unk> s".
In 1945, H. M. Powell named these<unk> s<unk> .<unk>  complex used to refer only to the inclusion complex of hydroquinone, but recently it has been adopted for many complexes which consist of a host molecule (forming the basic frame) and a guest molecule (set in the host molecule by interaction).  The<unk>  complexes are various and include, for example, strong interaction via chemical bonds between host molecules and guest molecules, or guest molecules set in the geometrical space of host molecules by weak intermolecular force. Typical examples of host-guest complexes are inclusion<unk> s and intercalation<unk> .
The history of<unk> s is relatively new.<unk>  hydrates were discovered in 1810 by Sir Humphrey Davy.<unk> s were studied by P. Pfeiffer in 1927 and in 1930, E. Hertel defined molecular<unk> s as substances decomposed into individual components following the mass action law in solution or gas state.  Therefore, basic information about<unk> s (then called molecular<unk> s) was known in those days. The development of<unk> s was attained by analyzing crystal structure by Powell (mentioned above), and they were applied to the separation of paraffin using a urea or thiourea host. Thereafter, cyclodextrin, crown ether, and cryptand were found as host molecules (see figure). A much studied host molecule is Dianin's<unk> .
In analyzing and separating techniques, the concept of inclusion<unk> s has taken root and many applications of them are known. It is possible to isolate not only chemically different species but also structural isomers, positional isomers (enantiomers and diastereomers), and radioactive isomers using<unk> s.
The structure of<unk> s is also related to the structure of foams (see Weaire-Phelan structure).
For a theory regarding the sudden release of methane<unk>  from ocean sediments see<unk>  gun hypothesis.
Clathrate compound
Diazonium compound
Organophosphate
Organothiophosphates
Detergent
Antimetabolite
Indole alkaloid
Protic solvent