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:
\(\ce{(C5H5)2Fe}\ (\rm{ferrocene})\) = \(\ce{bis(\upeta^{5}{-}cyclopentadienyl)iron}\), where \(\upeta^{5}\) can be read as eta-five or pentahapto.
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)