Hapticity (${\eta }^n$)

Hapticity, written ${\eta }^n$, specifies the number of contiguous ligand atoms involved in attachment to a metal. It differs from denticity, which counts donor sites in a chelate.

A change in the number of adjacent ring atoms coordinating a metal, such as ${\eta }^5\to {\eta }^3$. It changes the coordination ligand donation and can open a site without loss of the entire ring coordination ligand.