Macrocyclic ligand

In coordination chemistry, a macrocyclic ligand is a macrocyclic ring having at least nine atoms (including all hetero atoms) and three or more donor sites that serve as ligands that can bind to a central metal ion. Crown ethers and porphyrins are prominent examples. Macrocyclic ligands exhibit high affinity for metal ions. Porphyrins and phthalocyanines have long been recognized as potent ligands in coordination chemistry as illustrated by numerous transition metal porphyrin complexes and the commercialization of copper phthalocyanine pigments. In the 1960s the synthesis of macrocylic ligands received much attention. One early contribution involved the synthesis of the "Curtis macrocycles", in which a metal ion serves as a template for ring formation. Polyether macrocycles - or "crown" ligands - were also developed at that time. A few years later, three-dimensional analogs of crown ethers called "cryptands" were reported by Lehn and co-workers. Ag(18-ane-S6) dication.png|The silver complex of a [[thia-crown ether]] [Ag(18-ane-S6)]2+ Cyclen Zinc InorgChem 1997 4579 commons.jpg|Crystal structure of a Zn(II)-[[cyclen]]-[[ethanol]] dication.{{cite journal|title=Fixation of CO2 by Zinc(II) Chelates in Alcoholic Medium. X-ray Structures of {[Zn(cyclen)]3(μ3-CO3)}(ClO4)4 and Zn(cyclen)EtOH2|authors=Antje Schrodt, Anton Neubrand, Rudi van Eldik|journal=Inorg. Chem.|year=1997|volume=36|issue=20|pages=4579–4584|doi=10.1021/ic961368t|pmid=11670124}} FeTAML.png|Fe-[[tetra-amido macrocyclic ligand|TAML complex]].{{citation |last1=Collins |first1=T. J. |year=2002 |title=TAML oxidant activators: a new approach to the activation of hydrogen peroxide for environmentally significant problems |journal=Accounts of Chemical Research |volume=35 |issue=9 |pages=782–790 |doi=10.1021/ar010079s |pmid=12234208 }} 1,4,7-triazacyclononane.svg|[[1,4,7-Triazacyclononane]] is a tridentate ligand, which is prepared without metal templating.