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NEET · Chemistry · STD 12 - 5. Co-ordination chemistry

Which of the following has longest \(C-O\) bond length ? (Free \(C-O\) bond length in \(CO\) is \(1.128\,\mathop A\limits^o .\))

  1. A \([Fe(CO)_4]^{2-}\)
  2. B \([Mn(CO)_6]^+\)
  3. C \(Ni(CO)_4\)
  4. D \([Co(CO)_4]^-\)
Verified Solution

Answer & Solution

Correct Answer

(A) \([Fe(CO)_4]^{2-}\)

Step-by-step Solution

Detailed explanation

As the negative charge on metal carbonyl complex increases back pi bonding increases and hence the bond length of \(\mathrm{C}-O\) bond increases while the bond length of metal-carbon bond decreases. Hence. [Fe(CO), \(] ^{2-} {\text { has longest } C-O \text { bond length }}\) among the given complexes. The correct order of bond length of the given complexes is \(\left[\mathrm{Mn}(\mathrm{CO})_{6}\right]^{+} < { \left[\mathrm{Ni}(\mathrm{CO})_{4}\right]}<\left[\mathrm{Co}(\mathrm{CO})_{4}\right]^{-}<\left[\mathrm{Fe}(\mathrm{CO})_{4}\right]^{2-}\)