Question

In which of the following coordination entities the magnitude of $\Delta_0$ (CFSE in octahedral field) will be maximum? (At. no. of Co = 27)

• A. ${[Co (H20)6]^{3+}}$
• B. $[Co(NH_3)_6]^{3+}$
• C. $[Co (CN)_6]^{3-}$
• D. $[Co(C_2O_4)_3]^{3-}$

Answer 1

The Correct Option is C

 The question asks about the magnitude of \(\Delta_0\) in coordination complexes. \(\Delta_0\) is the Crystal Field Splitting Energy for octahedral complexes. This is determined by the nature of the ligands according to the spectrochemical series, where ligands are arranged based on their field strength.

1. Understanding the spectrochemical series: Ligands cause different magnitudes of splitting of the d-orbitals in an octahedral field. The stronger the ligand, the larger the value of \(\Delta_0\).
2. Spectrochemical series: CN^- > NO₂^- > en > NH₃ > H₂O > Br^- > I^-
3. In the given coordination complexes:
   • \({[Co (H_2O)_6]^{3+}}\): Water (H₂O) is a relatively weak ligand.
   • \([Co(NH_3)_6]^{3+}\): Ammonia (NH₃) is a stronger ligand than water, but weaker than CN^-.
   • \([Co (CN)_6]^{3-}\): Cyanide (CN^-) is a very strong ligand, causing significant splitting.
   • \([Co(C_2O_4)_3]^{3-}\): Oxalate (C₂O₄^2-) is weaker compared to CN^-.
4. Conclusion: Among the given complexes, \([Co (CN)_6]^{3-}\) has the strongest ligand, which is CN^-. Therefore, it will have the maximum crystal field splitting energy, \(\Delta_0\).
5. \([Co (CN)_6]^{3-}\) is indeed the correct answer.

Ultimately, \([Co (CN)_6]^{3-}\) has the highest magnitude of \(\Delta_0\) due to the strong cyanide ligand, confirming it as the correct option in this context.