The assembling of separate
molecular entities into any aggregate, especially of oppositely charged free ions into
ion pairs or larger and not necessarily well-defined clusters of ions held together by electrostatic
attraction. The term signifies the reverse of
dissociation, but is not commonly used for the formation of definite
adducts by
colligation or
coordination.
Source:
PAC, 1994, 66, 1077
(Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994))
on page 1086