ligands have only one salicylimine group. They are prepared from a salicylaldehyde and a monoamine. The name “salen” or “salen-type” may be used for other ligands that have similar environment around the chelating site, namely two acidic hydroxyls and two Schiff base (aryl-imine) groups. These include the ligands abbreviated as salph, from the condensation of 1,2-phenylenediamine and salicylaldehyde, and salqu, from the condensation of salicylaldehyde and 2-quinoxalinol. See also Metal salen complexes Bisthiosemicarbazones, a structurally related class of C2-symmetric imine based ligands References Organometallic chemistry Schiff bases Tetradentate ligands