In which of the following octahedral complex species the magnitude of $\Delta_0$ will be maximum?

In which of the following octahedral complex species the magnitude of $\Delta_0$ will be maximum?
  1. $\left[\mathrm{Co}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}$
  2. $\left[\mathrm{Co}(\mathrm{CN})_6\right]^{3-}$
  3. $\left[\mathrm{Co}\left(\mathrm{C}_2 \mathrm{O}_4\right)_3\right]^{3-}$
  4. $\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}$

Solution

Crystal field splitting depends upon the nature of ligand. The nature of ligand $\Delta$ decreases as shown below $\mathrm{C}_2 \mathrm{O}_4^{--} < \mathrm{H}_2 \mathrm{O} < \mathrm{NH}_3 < \mathrm{CN}^{-}$ hence the crystal field splitting will be maximum for $\left[\mathrm{Co}(\mathrm{CN})_6\right]^{3-}$

Asked in: JEE Main 2013 (25 Apr Online)

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