Title: complex
Long Title: IUPAC Gold Book - complex
DOI: 10.1351/goldbook.C01203
Status: current

Definition
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'.

Related Terms
- activated complex: https://goldbook.iupac.org//terms/view/A00092
- adduct: https://goldbook.iupac.org//terms/view/A00138
- association: https://goldbook.iupac.org//terms/view/A00472
- bond: https://goldbook.iupac.org//terms/view/B00697
- charge-transfer complex: https://goldbook.iupac.org//terms/view/C01003
- chemical species: https://goldbook.iupac.org//terms/view/CT01038
- coordination entity: https://goldbook.iupac.org//terms/view/C01330
- electron-donor-acceptor complex: https://goldbook.iupac.org//terms/view/E01989
- encounter complex: https://goldbook.iupac.org//terms/view/E02087
- inclusion compound: https://goldbook.iupac.org//terms/view/I02998
- molecular entity: https://goldbook.iupac.org//terms/view/M03986
- transition state: https://goldbook.iupac.org//terms/view/T06468
- π-adduct: https://goldbook.iupac.org//terms/view/A04388
- σ-adduct: https://goldbook.iupac.org//terms/view/A05436

Source
- PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1098 (https://doi.org/10.1351/pac199466051077)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/C01203/html
- json: https://goldbook.iupac.org/terms/view/C01203/json
- xml: https://goldbook.iupac.org/terms/view/C01203/xml

Citation: Citation: 'complex' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.C01203
License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms.
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Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.
Accessed: 2025-10-05T05:32:24+00:00