Salen refers to a tetradentate C2-symmetric ligand synthesized from salicylaldehyde (sal) and ethylenediamine (en).

It may also refer to a class of compounds, which are structurally related to the classical salen ligand, primarily bis-Schiff bases.

Salen ligands are notable for coordinating a wide range of different metals, which they can often stabilise in various oxidation states.

[1] For this reason salen-type compounds are used as metal deactivators.

[3] Complexes of salen with metal cations can often be made in situ, i.e., without isolating the H2salen.