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Question: Answered & Verified by Expert
In which of the following complex ion, the central metal ion is in a state of $s p^{3} d^{2}$ hybridisation?
ChemistryCoordination CompoundsCOMEDKCOMEDK 2018
Options:
  • A $\left[\mathrm{CoF}_{6}\right]^{3-}$
  • B $\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+}$
  • C $\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-}$
  • D $\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+}$
Solution:
1039 Upvotes Verified Answer
The correct answer is: $\left[\mathrm{CoF}_{6}\right]^{3-}$
In $\left[\mathrm{CoF}_{6}\right]^{3-}, \mathrm{F}^{-}$is a weak ligand. It cannot pair up $d$-electrons and form outer orbital octahedral complex while $\mathrm{NH}_{3}$ and $\mathrm{CN}^{-}$are strong ligand.

In $\left[\mathrm{CoF}_{6}\right]^{3-}$, outer orbital $4 d$ is used in hybridisation. Thus, it is called outer orbital or high spin or spin free complex.
$$
\mathrm{Co}=[\mathrm{Ar}] 3 d^{7} 4 s^{2} \text { and } \mathrm{Co}^{3+}=[\mathrm{Ar}] 3 d^{6}
$$

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