The use of η to denote hapticity is systematised. The use of η is not recommended. When the specification of the atoms involved is ambiguous the position of the atoms must be specified. This is illustrated by the examples:
* Cr(η-CH), named as bis(η-benzene)chromium as all of the (contiguous) atoms in the benzene ligands are involved their position does not have to be specified
* [(1,2,5,6-η)-cycloocta-1,3,5,7-tetraene](η-cyclopentadienyl)cobalt in this only two (at positions 1 and 5) of the four double bonds are linked to the central atom.