Question

The value of CFSE $\left({\Delta }_o\right)$ for complexes given below follow the order:

(I) $\left[Co\right(N{H}_3{)}_6{]}^{3+}$ (II) $\left[Rh\right(N{H}_3{)}_6{]}^{3+}$ (III) $\left[Ir\right(N{H}_3{)}_6{]}^{3+}$

• A. I < II < III
• B. I > II > III
• C. I < II > III
• D. I=II=III

Answer 1

Answer: (A)

I < II < III

For the given complexes, the oxidation states of the central metal ions is same.

The ligands are also same. But the effective nuclear charge of the metal ions is different.

Higher is the value of the $Z_{eff}$, higher will be the value of CFSE ${(}_o)$ for complexes .

The $Z_{eff}$ value for the central metal ion in the complexes increases in the order

$\left[Co\right(N{H}_3{)}_6{]}^{3+}<\left[Rh\right(N{H}_3{)}_6{]}^{3+}<\left[Ir\right(N{H}_3{)}_6{]}^{3+}$.

The value of CFSE ${(}_o)$ for complexes follow the order $I<II<III$ or

$\left[Co\right(N{H}_3{)}_6{]}^{3+}<\left[Rh\right(N{H}_3{)}_6{]}^{3+}<\left[Ir\right(N{H}_3{)}_6{]}^{3+}$