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JEE Advanced · Chemistry · 23. Coordination Compounds

Among the following metal carbonyls, the \(\mathrm{C}-\mathrm{O}\) bond order is lowest in

  1. A \(\left[\mathrm{MO}(\mathrm{CO})_6\right]^{+}\)
  2. B \(\left[\mathrm{Fe}(\mathrm{CO})_5\right]\)
  3. C \(\left[\mathrm{Cr}(\mathrm{CO})_6\right]\)
  4. D \(\left[\mathrm{V}(\mathrm{CO})_6\right]^{-}\)
Verified Solution

Answer & Solution

Correct Answer

(B) \(\left[\mathrm{Fe}(\mathrm{CO})_5\right]\)

Step-by-step Solution

Detailed explanation

(a) \(\mathrm{Mn}^{+}=3 d^5 4 s^1\) In presence of \(\mathrm{CO}\) effective configuration \(=3 d^6 4 s^0, 3\) lone pair for back bonding with vacant orbital of \(\mathrm{C}\) in \(\mathrm{CO}\).
(b) \(\mathrm{Fe}^{\circ}=3 d^6 4 s^2\) in presence of \(\mathrm{CO}\) effective configuration \(=3 d^8, 4\) lone pair for back bonding with \(\mathrm{CO}\).
(c) \(\mathrm{Cr}^{\circ}=3 d^5 4 s^1\), effective configuration \(=3 d^6\)
3 lone pair for back bonding with \(\mathrm{CO}\).
(d) \(\mathrm{V}^{-}=3 d^4 s^2\), effective configuration \(=3 d^6, 3\) lone pair for back bonding with \(\mathrm{CO}\). Maximum back bonding in \(\mathrm{Fe}(\mathrm{CO})_5\), therefore \(\mathrm{CO}\) bond order is lowest here.
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