Hapticity is the
coordination of a
ligand to a metal center via an uninterrupted and contiguous series of
atoms. The hapticity of a ligand is described with the Greek letter
η ('eta'). For example, η
2 describes a ligand that coordinates through 2 contiguous atoms. In general the η-notation only applies when multiple atoms are coordinated (otherwise the
κ-notation is used). In addition, if the ligand coordinates through multiple atoms that are
not contiguous then this is considered
denticity (not hapticity), and the κ-notation is used once again. When naming complexes care should be taken not to confuse η with
μ ('mu'), which relates to
bridging ligands.