Macrocyclic ligand

One early contribution involved the synthesis of the "Curtis macrocycles", in which a metal ion serves as a template for ring formation.

[3] A few years later, three-dimensional analogs of crown ethers called "cryptands" were reported by Lehn and co-workers.

The size of the metal cation used as the template has proved to be of importance in directing the synthetic pathway for the Schiff base systems.

The compatibility between the radius of the template cation and the "hole" of the macrocycle contributes to the effectiveness of the synthetic pathway and to the geometry of the resulting complex.

[13] Heme, the active site in the hemoglobin (the metalloprotein in blood that transports oxygen), is a porphyrin that contains iron.

14-membered N4 macrocyclic ligands, called Curtis macrocycles, arise from the condensation of acetone and a nickel complex of ethylenediamine .
18-Crown-6 can be synthesized by the Williamson ether synthesis using potassium ion as the template cation.