Given below are two statements:
Statement I: The M – C \(\sigma\) bond is formed by the donation of lone pair of electrons on the carbonyl carbon into a vacant d-orbital of the metal
Statement II: The M – C \(\pi\) bond is formed by the donation of a pair of electrons from a filled d-orbital of metal into the vacant antibonding \(\pi\)* orbital of carbon monoxide.
In the light of the above statements, choose the correct answer from the options given below:
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Visualize synergic bonding as a "give and take" relationship.
\textbf{Ligand gives (\(\sigma\) bond):} CO donates its lone pair to the metal's empty orbital.
\textbf{Metal gives back (\(\pi\) bond):} The metal donates electrons from its filled d-orbital to CO's empty \(\pi\)* orbital.
This dual bonding mechanism is why CO is a strong field ligand and forms very stable complexes.
Statement I is correct but Statement II is incorrect
Statement I is incorrect but Statement II is correct
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The Correct Option isA
Solution and Explanation
Step 1: Understanding Synergic Bonding in Metal Carbonyls.
The bonding between a metal atom and a carbon monoxide (carbonyl) ligand is a special type of bonding called synergic bonding. It consists of two components: a sigma (\(\sigma\)) bond and a pi (\(\pi\)) bond. Step 2: Analyzing Statement I.
This statement describes the formation of the sigma bond. The carbon atom in the CO molecule has a lone pair of electrons. This lone pair is donated into a suitable vacant orbital of the metal atom (which can be a d-orbital, or a hybrid orbital). This forms a standard coordinate covalent bond, which is a \(\sigma\) bond. The direction of electron donation is from the ligand (CO) to the metal (M). So, M \(\leftarrow\) CO. Statement I accurately describes this process. Thus, Statement I is correct. Step 3: Analyzing Statement II.
This statement describes the formation of the pi bond, also known as back-bonding. The metal atom has filled d-orbitals. The CO ligand has vacant antibonding pi-star (\(\pi\)*) orbitals. A pair of electrons from a filled d-orbital of the metal is donated back into a vacant \(\pi\)* orbital of the CO ligand. This creates a \(\pi\) bond. The direction of electron donation is from the metal (M) to the ligand (CO). So, M \(\rightarrow\) CO. Statement II accurately describes this back-donation. Thus, Statement II is correct. Step 4: Conclusion.
Both statements correctly describe the two components of synergic bonding in metal carbonyls. The sigma bond strengthens the pi bond and vice-versa, leading to a strong overall M-C bond. Step 5: Final Answer.
Both Statement I and Statement II are correct.
