Title: formation constant
Long Title: IUPAC Gold Book - formation constant
DOI: 10.1351/goldbook.F02485
Status: current

Definition
For a mononuclear binary complex, if a central atom (central group) $\ce{M}$ (the 'metal') and a ligand $\ce{L}$ have been defined, then in the following expressions \(K_{n}\) is the stepwise formation constant, and \(\beta_{n}\) is the cumulative formation constant for the complex $\ce{ML_{n}}$. They can both be referred to as stability constants (stepwise and cumulative). \[K_{n}=K(\rm{ML}_{n- 1}+\rm{L}\rightleftharpoons \rm{ML}_{n})\] \[\beta_{n} = K(\rm{M}+n\rm{L}\rightleftharpoons \rm{ML}_{n})\]

Related Term
- central atom: https://goldbook.iupac.org//terms/view/C00930

Source
- Orange Book, 2nd ed., p. 11 (https://media.iupac.org/publications/analytical_compendium/)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/F02485/html
- json: https://goldbook.iupac.org/terms/view/F02485/json
- xml: https://goldbook.iupac.org/terms/view/F02485/xml

Citation: Citation: 'formation constant' 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.F02485
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.
Collection: If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .
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: 2026-06-30T05:10:00+00:00