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Question #44597

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The Question

Consider the neutral homoleptic carbonyl $V(CO)_6$ and its reduced anionic form $[V(CO)_6]^-$ at $298\text{ K}$ . Which of the following statements correctly describes their electronic stability, adherence to the Effective Atomic Number (EAN) rule, and structural parameters?

Options

A.
$V(CO)_6$ dimerizes to $V_2(CO)_{12}$ to satisfy the EAN rule, making it diamagnetic with a shorter $V-C$ bond length than $[V(CO)_6]^-$ .
B.
$V(CO)_6$ is a stable, paramagnetic 17-electron radical that violates the EAN rule, and it possesses a longer $V-C$ bond length compared to $[V(CO)_6]^-$ .
C.
Both species obey the EAN rule because $CO$ acts as a 3-electron donor in $V(CO)_6$ via bridging, resulting in equal $V-C$ bond lengths.
D.
$V(CO)_6$ violates the EAN rule but exhibits a shorter $V-C$ bond length than $[V(CO)_6]^-$ due to the absence of interelectronic repulsion in the metal $d$ -orbitals.

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Exception_Exposure

Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.

Concepts Behind This Question

EAN Rule (Sidgwick's Rule)|Valence Bond Theory Hybridization|Crystal Field Splitting (Octahedral)

Why This Question Is Tricky

Common Mistakes

This question tests a classic exception to the EAN/18-electron rule and the nuances of synergic bonding.

Students often assume that all stable metal carbonyls must obey the EAN rule, either by default or by dimerization (like $Mn_2(CO)_{10}$ ). $V(CO)_6$ is the primary exception: a sterically constrained 17-electron radical that cannot dimerize.

Furthermore, the trap exploits the conflation of oxidation state effects on backbonding; students may incorrectly assume a neutral metal forms stronger/shorter bonds than an anionic metal due to electrostatics, ignoring the dominant $\pi$ -backbonding effect where increased electron density (anionic charge) strengthens the M-C bond and shortens it.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Coordination Compounds - Class 12
Concept	EAN Rule (Sidgwick's Rule)
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free