In which of the following coordination entities the magnitude of $\Delta \mathrm{O}$ (CFSE in octahedral…

In which of the following coordination entities the magnitude of $\Delta \mathrm{O}$ (CFSE in octahedral field) will be maximum (at. no. $\mathrm{Co}=27$ )?
  1. $\left[\mathrm{Co}\left(\mathrm{C}_2 \mathrm{O}_4\right)_3\right]^{3-}$
  2. $\left[\mathrm{Co}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{3+}$
  3. $\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}$
  4. $\left[\mathrm{Co}(\mathrm{CN})_6\right]^{3-}$

Solution

As in all the given complex the central metal atom is same and contains same number of \(d\) electrons, thus CFSE is decided by ligands. In case of strong field ligand, CFSE is maximum. \(C N^{-}\) is a strong field ligand, is maximum. The magnitude of \(\Delta_{\text {oct }}\) will be maximum in \(\left[\mathrm{Co}(\mathrm{CN})_6\right]^{3-}\). Hence, in \(\left[\mathrm{Co}(\mathrm{CN})_6\right]^{3-} \mathrm{CFSE}\)

Asked in: NEET 2008 (Mains)

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