Term: hapticity
https://doi.org/10.1351/goldbook.08174

Definition:
Topological description for the number of contiguous atoms of a ligand that are bonded to a central metal atom.

Note: The hapticity is indicated as a superscript following the Greek letter \(\upeta\).

Example: <span title="substance">\(\ce{(C5H5)2Fe}\ (\rm{ferrocene})\)</span> = <span title="substance">\(\ce{bis(\upeta^{5}{-}cyclopentadienyl)iron}\)</span>, where <span title="symbol">\(\upeta^{5}\)</span> can be read as eta-five or pentahapto.

Example: Array

Source: PAC, 2022, 94, 353. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 2021)' on page 429 (https://doi.org/10.1515/pac-2018-1010)

Citation: 'hapticity' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.08174

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.

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.