Hapticity

Under the hapticity a ligand in coordination chemistry is understood the number of ligand atoms that are directly bonded to the central atom of a complex. The indication of hapticity provides information about different binding states of a ligand when more atoms are binding available.

Ligands, which can contribute to the binding of different number of atoms are, for example, unsaturated organic molecules, such as allyl ( C3H5 ), benzene ( C6H6 ), or cyclopentadienyl ( C5H5 ).

The appointment shall be made by the letter ηn (Greek eta ), which is prefixed to the name of the complex. The superscript n indicates the number of bound atoms. You ηn reads as n- hapto ( η3 = trihapto, η4 = tetrahapto, η5 = pentahapto, etc.).

The often hapticity of ligands changes with substitution or redox reactions: