Question

In the complex \[{[Fe{({H_2}O)_6}]^{3 + }}\] , \[{[Fe{(SCN)_6}]^{3 - }}\] , \[{[Fe{({C_2}{O_4})_3}]^{3 - }}\] and \[{[FeC{l_6}]^{3 - }}\] more stability is shown by:
A. \[{[Fe{({H_2}O)_6}]^{3 + }}\]
B. \[{[Fe{(SCN)_6}]^{3 - }}\]
C. \[{[Fe{({C_2}{O_4})_3}]^{3 - }}\]
D.\[{[FeC{l_6}]^{3 - }}\]

Answer 1

Hint: Chelates: There are various ligands that are polydentate in nature. Being polydentate means they have the ability to bond with a single central metal atom or ion, from two or more sites within the ligand. This means that polydentate ligands should have two or more than two donor sites. A chelate can be identified as an organic compound which is formed when a polydentate ligand is bonded to a central metal atom or ion. To put it in simpler terms, chelation can be understood as the process which forms two or more coordinate bonds between the central atom and the ligand.

Complete step by step answer:
The stability of complexes is directly proportional the number of chelates present in them. The higher the number of chelates, higher is the stability of the complex. Now let us observe the complexes given above:
  \[{[Fe{({H_2}O)_6}]^{3 + }}\] : This compound contains only one type of ligand, \[{H_2}O\] , which is a monodentate ligand.
  \[{[Fe{(SCN)_6}]^{3 - }}\] : This compound also contains only one type ligand, SCN, which is a monodentate ligand
  \[{[Fe{({C_2}{O_4})_3}]^{3 - }}\] : This compound contains one type of ligand, \[{C_2}{O_4}\] . This ligand is a bidentate ligand and is capable of chelation.
  \[{[FeC{l_6}]^{3 - }}\] : This compound also contains only one type ligand, Cl, which is a monodentate ligand
As we can see, only one complex has chelates present in it. This means that this is the most stable complex from the given options is \[{[Fe{({C_2}{O_4})_3}]^{3 - }}\]

Hence, Option C is the correct option.

Note:
Chelation may be defined as an equilibrium reaction between a metal ion and a complexing agent, characterized by the formation of more than one bond between the metal and a molecule of the complexing agent and resulting in the formation of a ring structure incorporating the metal ion.