Question

Given below are two statements: One is labelled as "Assertion A" and the other is labelled as "Reason R".
Assertion A: In the complex Ni(CO), and Fe(CO)s, the metals have zero oxidation state.
Reason R: Low oxidation states are found when a complex has ligands capable of π-donor character in addition to the o-bonding.
In the light of the above statements, choose the most appropriate answer from the option given below.

• A. Both A and R are correct and R is the correct explanation of A.
• B. Both A and R are correct but R is NOT the correct explanation of A
• C. A is correct but R is not correct
• D. A is not correct but R is correct

Answer 1

The Correct Option is C

Coordination Compound Oxidation States Analysis 

Let's analyze both Assertion A and Reason R:

Assertion A: In \( \text{Ni(CO)}_4 \) and \( \text{Fe(CO)}_5 \), the carbonyl ligand (\( \text{CO} \)) is neutral. Thus, the oxidation state of Ni and Fe in these complexes is indeed zero. So, Assertion A is correct.

Reason R: Low oxidation states of metals are stabilized by synergistic bonding, also known as backbonding. This involves σ-donation from the ligand to the metal and π-backdonation from the metal to the ligand. Crucially, the ligand must have empty π orbitals to accept electrons from the metal. \( \text{CO} \) is a π-acceptor ligand, not a π-donor ligand. So, Reason R is incorrect.

Conclusion:

The correct answer is (3): A is correct, but R is not correct.

Answer 2

The oxidation states of Ni and Fe in Ni(CO)\(_4\) and Fe(CO)\(_5\) are indeed zero. However, while low oxidation states can be stabilized by \(\pi\)-acceptor ligands, this is not the reason why Ni and Fe exhibit zero oxidation states in these complexes.