નીચેના પૈકી શામાં \(C-O\) બંધલંબાઇ સૌથી વધુ છે ? (મુક્ત \(CO\) માં \(C-O\) બંધલંબાઇ \(1.128\,\mathop A\limits^o \) છે.

A \([Fe(CO)_4]^{2-}\)
B \([Mn(CO)_6]^+\)
C \(Ni(CO)_4\)
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 \(\left[\mathrm{Mn}(\mathrm{CO})_{6}\right]^{+} < { \left[\mathrm{Ni}(\mathrm{CO})_{4}\right]}<\left[\mathrm{Co}(\mathrm{CO})_{4}\right]^{-}<\left[\mathrm{Fe}(\mathrm{CO})_{4}\right]^{2-}\)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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