Question

The complex that violates the Sidwick’s rule of EAN is:
A. Potassium Ferrocyanide
B. Hexamine Cobalt (III) Chloride
C. Tetra mine copper (II) sulphate
D. Potassium dichlorobis oxalato cobaltate (III)

Answer 1

Hint: To solve this question we need to understand the basics of EAN rule. According to Sidgwick central metal ion Effective Atomic Number i.e., EAN rule is the total number of electrons that surround the nucleus of an atom in a metal ion.

Complete step by step answer:
We know the formula of Effective Atomic Number is = $Z-X+2\times Y$
Where,
 Z is the atomic number of the metal,
X is the oxidation number and Y is the coordination number.
Here, we need to understand that the oxidation number is the total number of electrons that are lost in iron formation and coordination number is the total number of electrons that are gained from the donor atoms.
Now, we will individually find the value of the four options:
Potassium Ferrocyanide = $[Fe(CN{)}_6{]}^{4-}$
In the complex, we can see that the oxidation state of the metal ion is +2
We know the atomic number of iron is 26 and the coordination number is 6
Thus, EAN rule = $$\left(26-2\right)+(6\times 2)=36$$
Therefore, it is the atomic number of the nearest noble gas Kr (36).
B. Hexamine Cobalt (III) Chloride = $[Co(N{H}_3{)}_6{]}^{3+}$
In the complex, we can see that the oxidation state of the metal ion is +3
We know the atomic number of iron is 27 and the coordination number is 6
Thus, EAN rule = $$\left(27-3\right)+(6\times 2)=36$$
Therefore, it is the atomic number of the nearest noble gas Kr (36).
C. Tetra mine copper (II) sulphate = $[Cu(N{H}_3{)}_4{]}^{2+}$
In the complex, we can see that the oxidation state of the metal ion = +2
We know the atomic number of iron is 27 and the coordination number is 8
Thus, EAN rule = $$\left(27-2\right)+(4\times 2)=33$$
Therefore, it is an exception to the Sidwicks EAN rule.
D. Potassium dichlorobis oxalato cobaltate (III) = $K_3[Co(C_2{O}_4{)}_{2}C{l}_2{]}^{3+}$
In the complex, we can see that the oxidation state of the metal ion = +3
We know the atomic number of iron is 27 and the coordination number is 2, 4
Thus, EAN rule =$$\left(27-3\right)+(2\times 2)+(4\times 2)=36$$
Therefore, it is the atomic number of the nearest noble gas Kr (36).

Hence, Option C is the correct answer.

Note:
We must know that the EAN rule is also referred to as the 18-electron rule as the nine valence orbital can accommodate only 18 electrons. And also in coordination complex, we can calculate the number of ligands that are attached to the central metal ion with the help of this theory.