Hapticity

In addition, if the ligand coordinates through multiple atoms that are not contiguous then this is considered denticity[2] (not hapticity), and the κ-notation is used once again.

[3] When naming complexes care should be taken not to confuse η with μ ('mu'), which relates to bridging ligands.

Cotton later proposed the term hapticity derived from the adjectival prefix hapto (from the Greek haptein, to fasten, denoting contact or combination) placed before the name of the olefin,[7] where the Greek letter η (eta) is used to denote the number of contiguous atoms of a ligand that bind to a metal center.

The term is usually employed to refer to ligands containing extended π-systems or where agostic bonding is not obvious from the formula.

If the coordinating atoms are contiguous (connected to each other), the η-notation is used, as e.g. in titanocene dichloride: dichlorobis(η5-2,4-cyclopentadien-1-yl)titanium.