A
molecular entity comprising a cyclic or polycyclic assembly of
binding sites that contains three or more binding sites held together by
covalent bonds, and which defines a molecular cavity in such a way as to bind (and thus '
hide' in the cavity) another molecular entity, the
guest (a
cation, an
anion or a neutral species), more strongly than do the separate parts of the assembly (at
the same total concentration of binding sites). The
adduct thus formed is called a '
cryptate'. The term is usually restricted to bicyclic or oligocyclic molecular entities. Example:
Corresponding monocyclic ligand assemblies
crowns are sometimes included in this group, if they can be considered to define a cavity
in which a
guest can hide. The terms '
podand' and '
spherand' are used for certain specific ligand assemblies. Coplanar cyclic polydentate
ligands, such as
porphyrins, are not normally regarded as cryptands.
Source:
PAC, 1994, 66, 1077
(Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994))
on page 1102
PAC, 1995, 67, 1307
(Glossary of class names of organic compounds and reactivity intermediates based on
structure (IUPAC Recommendations 1995))
on page 1329
