Question

What do you understand by macrocyclic effect?

Answer 1

Macrocyclic effect is similar to chelating effect. This effect is seen during the formation of coordination compounds. These compounds are in cyclic structure for stability. In this coordination compounds are formed by the addition of ligands.

Complete answer:
Macrocyclic effect is when multidentate ligands form a cyclic ring with central metal atom or ion, as it is a multidentate ligand it enhances the stability of the complexes. Macrocyclic effect is the high affinity of metal cations for macrocyclic ligands, compared to their acyclic analogues. A macrocyclic ligand is a macrocycle with a ring size of at least nine (including all hetero atoms) and three or more donor sites. Macrocyclic ligands are not only multi-dentate, but because they are covalently constrained to their cyclic form, they allow less conformational freedom. Macrocyclic ligand can’t dissociate through a simple mechanism because there is no end group. Examples of macrocyclic ligands are crown ethers and porphyrins. The magnitude of macrocyclic effect depends on the ligand and metal center. The enhanced stability of a macrocyclic ligand complex may arise from its rate of dissociation being slow compared to its open chain analogue. Macrocyclic complexes are synthesized by combining macrocyclic ligands and metal ions. Macrocyclic ligands occur in many cofactors in proteins and enzymes. The natural occurrences of these complexes are Heme, the active site in the haemoglobin (the protein in blood that transports oxygen), is a porphyrin-containing iron. Chlorophyll, the green photosynthetic pigment found in plants, contains a chlorine ring.

Additional information:
Macrocyclic effect is seen in coordination compounds. It forms cyclic compounds for the stability of the complex. In this multidentate ligands are forming complexes with metal ions. Different compounds show different properties.

Note: Macrocyclic complexes have greater stability than acyclic complexes because they form cyclic compounds. For the dissociation of these complexes a great amount of energy is required as it is a complex mechanism. These complexes are highly used in various industries for different purposes.