Question

What are chelates? Give one example and write the importance of chelate?

Answer 1

A ligand is a molecule or an ion that is attached to the metal atom by a coordinate bonding. It donates its electron pair to form a complex. Ligands can be anionic, cationic, or neutral. Ligand acts as a Lewis base and the central metal atom acts as Lewis acid. The examples of ligands are ${\text{N}}{{\text{O}}^{\text{ + }}}$, ${{\text{F}}^{\text{ - }}}$, ${\text{N}}{{\text{H}}_{\text{3}}}$, etc, There are different types of ligands called as monodentate, bidentate, polydentate depending on the binding sites. If the ligand is bonded to the metal through one atom, it is called a monodentate ligand. Bidentate ligands have 2 atoms that can bind to the central atom at 2 points. This means that it can donate 2 pairs of electrons.
Complete step by step answer:
Now, we know what a bidentate ligand is. Here, the Ligand has 2 donor sites.
Example:- en- ethylenediamine.
${\text{N}}{{\text{H}}_{\text{2}}}{\text{--C}}{{\text{H}}_{\text{2}}}{\text{--C}}{{\text{H}}_{\text{2}}}{\text{--N}}{{\text{H}}_{\text{2}}}$
We know there is one lone pair of electrons on both the N atoms.
Thus, both the N can be coordinated to the central metal atom.

Another example of the polydentate ligand is ethylenediaminetetraacetic acid (EDTA) which is a hexadentate ligand. It leads to the formation of the ring.
Chelation is a process in which a bidentate or a polydentate ligand binds to the metal atom to form a ring.
The complex formed by this process is called a chelate.
The polydentate ligand which leads to chelation is called a chelating agent.
The importance of chelate is:-
It is used in chelation therapy to remove toxic substances from the body (in lead poisoning)
It is used as a contrast agent in MRI scanning.
It is used in chemical water treatments to remove metals.
They can also be used to separate lanthanides and actinides.

Note: As we discussed monodentate ligand donates a lone pair of electrons and bind to the central atom at one point. ${{\text{[Cu(N}}{{\text{H}}_{\text{3}}}{{\text{)}}_{\text{6}}}{\text{]}}^{{\text{2 + }}}}$. Here each ${\text{N}}{{\text{H}}_{\text{3}}}$ group is linked to the metal by only one atom. In the above complexes, ” $\to$ ” shows the coordinate bond. A complex $[CaN{a_2}EDTA]$ is given to a person who has consumed lead. The lead present in the bloodstream forms a complex $[PbN{a_2}EDTA]$ and Ca is left behind. $[PbN{a_2}EDTA]$ is more stable and complex and excreted. The chelating complex also has an application in agriculture.