Question

The order of the M–C bond strength in the following species is (Atomic number for Cr = 24, Mn = 25, Ti = 22, Co = 27)
\[ \text{[Cr(CO)}_6] \text{[Mn(CO)}_6]^+ \text{[Ti(CO)}_6]^{2-} \text{[Co(CO)}_6]^+ \]

• A. II > I > IV > III
• B. I > III > II > IV
• C. III > IV > I > II
• D. III > I > II > IV

Hint:

A metal in a lower oxidation state generally has a stronger M–C bond due to greater electron density and enhanced \(\pi\)-back donation to the CO ligands.

Answer 1

The Correct Option is C

Step 1: Understanding the bonding.
The bond strength between metal and carbon (M–C bond strength) is influenced by the metal's oxidation state, the nature of the metal, and the metal's ability to donate electron density to the \(\pi\)-accepting CO ligands. The more electron-rich the metal, the stronger the M–C bond due to increased electron donation to the CO.

Step 2: Analyzing the species.
- For [Cr(CO)6], Cr is in the 0 oxidation state, with a relatively high electron density on the metal. This results in a strong M–C bond.
- [Mn(CO)6]+ has Mn in the +1 oxidation state, reducing the electron density and weakening the M–C bond compared to Cr.
- [Ti(CO)6]2- has Ti in the +2 oxidation state, further reducing the electron density and weakening the M–C bond compared to Mn and Cr.
- [Co(CO)6]+ has Co in the +1 oxidation state, which gives it the least electron density and the weakest M–C bond among the given species.

Step 3: Conclusion.
The order of M–C bond strength is III > I > II > IV, so the correct answer is (D).