A metal salen complex is a coordination compound between a metal cation and a ligand derived from N,N′-bis(salicylidene)ethylenediamine, commonly called salen. The classical example is salcomine, the complex with divalent cobalt , usually denoted as Co(salen). These complexes are widely investigated as catalysts and enzyme mimics.
The metal-free salen compound (Hsalen or salenH) has two phenolic hydroxyl groups. The salen ligand is usually its conjugate base (salen), resulting from the loss of protons from those hydroxyl groups. The metal atom usually makes four coordination bonds to the oxygen and nitrogen atoms.