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In supramolecular chemistry, [1] host–guest chemistry describes complexes that are composed of two or more molecules or ions that are held together in unique structural relationships by forces other than those of full covalent bonds. Host–guest chemistry encompasses the idea of molecular recognition and interactions through non-covalent ...
In host–guest chemistry the bistable states of molecular switches differ in their affinity for guests. Many early examples of such systems are based on crown ether chemistry. The first switchable host is described in 1978 by Desvergne & Bouas-Laurent [10] [11] who create a crown ether via photochemical anthracene dimerization.
Coordination cages are used to study guest-guest and host–guest interactions and reactions. In some instance, planar aromatic molecules stack inside of metalloprisms, as can be observed by UV-visible spectroscopy. Metal-metal interactions can also be observed. [15] Mixed valence species have also been trapped inside of coordination cages. [15]
Most clathrate compounds are polymeric and completely envelop the guest molecule, but in modern usage clathrates also include host–guest complexes and inclusion compounds. [2] According to IUPAC, clathrates are inclusion compounds "in which the guest molecule is in a cage formed by the host molecule or by a lattice of host molecules."
Crystal structure of a nitrobenzene bound within a hemicarcerand reported by Cram and coworkers in Chem. Commun., 1997, 1303-1304.. In host–guest chemistry, a carcerand (from Latin carcer 'prison') is a host molecule that completely entraps its guest (which can be an ion, atom or other chemical species) so that it will not escape even at high temperatures. [1]
In terms of supramolecular chemistry, chemosensing is an example of host–guest chemistry, where the presence of a guest (the analyte) at the host site (the sensor) gives rise to recognition event (e.g. sensing) that can be monitored in real time.
Static molecular recognition is likened to the interaction between a key and a keyhole; it is a 1:1 type complexation reaction between a host molecule and a guest molecule to form a host–guest complex. To achieve advanced static molecular recognition, it is necessary to make recognition sites that are specific for guest molecules.
One famous intercalation host is graphite, which intercalates potassium as a guest. [3] Intercalation expands the van der Waals gap between sheets, which requires energy. Usually this energy is supplied by charge transfer between the guest and the host solid, i.e., redox. Two potassium graphite compounds are KC 8 and KC 24.