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Question #44347

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The Question

Consider the substitution of one carbonyl ligand in the ideal tetrahedral complex \ce{[Ni(CO)4]} by a highly electronegative fluoride ion to form the complex anion \ce{[Ni(CO)3F]-} at 298 K. Based on Bent's Rule and the electronic properties of the ligands, determine the expected distortion in the $C-Ni-C$ bond angle ( $\theta$ ) relative to the ideal tetrahedral angle ( $109.5^\circ$ ), the number of IR-active $\nu_{CO}$ stretching bands, and the shift in the average $\nu_{CO}$ stretching frequency relative to \ce{[Ni(CO)4]}.

Options

A.
$\theta > 109.5^\circ$ ; 2 IR bands ; Lower $\nu_{CO}$
B.
$\theta < 109.5^\circ$ ; 2 IR bands ; Higher $\nu_{CO}$
C.
$\theta > 109.5^\circ$ ; 3 IR bands ; Higher $\nu_{CO}$
D.
$\theta < 109.5^\circ$ ; 1 IR band ; Lower $\nu_{CO}$

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.

Concepts Behind This Question

Bent's Rule|Ligand Denticity Variations|Tetrahedral Splitting Patterns

Why This Question Is Tricky

Common Mistakes

This problem tests the intersection of Bent's Rule, Group Theory (IR spectroscopy), and Organometallic electronic effects.

The primary trap is assuming the highly electronegative F atom or its lone pairs exert greater steric/electronic repulsion (incorrectly predicting $\theta < 109.5^\circ$ ).

In reality, both VSEPR (electronegative substituents have smaller bond pair domains) and Bent's Rule (F draws p-character, leaving s-character to widen the C-Ni-C angle) predict $\theta > 109.5^\circ$ .

Additionally, students often miscount IR bands by ignoring $C_{3v}$ symmetry rules (guessing 3 independent bands) or fail to recognize that the overall anionic charge dominates the $\pi$ -backbonding extent, lowering the stretching frequency despite F being an electronegative atom.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Chemical Bonding and Molecular Structure - Class 11 Part 1
Concept	Bent's Rule
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free