A molecular entity formed by loose association involving two or more component molecular entities (ionic or uncharged), or the corresponding chemical species. The bonding between the components is normally weaker than in a covalent bond. The term has also been used with a variety of shades of meaning in different contexts: it is therefore best avoided when a more explicit alternative is applicable. In inorganic chemistry the term 'coordination entity' is recommended instead of 'complex'.
See also: activated complex, adduct, charge-transfer complex, electron-donor-acceptor complex, encounter complex, inclusion compound, σ-adduct, π-adduct, transition state
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1098 (https://doi.org/10.1351/pac199466051077)