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Question #44202

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The Question

Consider the isoelectronic series of octahedral metal carbonyl complexes: $[Ti(CO)_6]^{2-}$ , $[V(CO)_6]^-$ , $[Cr(CO)_6]$ , and $[Mn(CO)_6]^+$ . Their observed C-O stretching frequencies ( $\nu_{CO}$ ) are $1748 \text{ cm}^{-1}$ , $1859 \text{ cm}^{-1}$ , $2000 \text{ cm}^{-1}$ , and $2094 \text{ cm}^{-1}$ (not necessarily in this order). Separately, consider the silyl and alkyl amines, $N(SiH_3)_3$ and $N(CH_3)_3$ . Which of the following options correctly identifies: (i) The $\nu_{CO}$ of $[V(CO)_6]^-$ , (ii) The complex possessing the shortest M-C bond length, and (iii) The hybridization of the central nitrogen atom in $N(SiH_3)_3$ and $N(CH_3)_3$ , respectively?

Options

A.
$1859 \text{ cm}^{-1}$ , $[Ti(CO)_6]^{2-}$ , $sp^2$ and $sp^3$
B.
$1859 \text{ cm}^{-1}$ , $[Mn(CO)_6]^+$ , $sp^3$ and $sp^3$
C.
$2000 \text{ cm}^{-1}$ , $[Ti(CO)_6]^{2-}$ , $sp^2$ and $sp^3$
D.
$1748 \text{ cm}^{-1}$ , $[Mn(CO)_6]^+$ , $sp^3$ and $sp^2$

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

Bond Angle Variations|Valence Bond Theory Hybridization|Synergic Bonding in Carbonyls

Why This Question Is Tricky

Common Mistakes

The question tests the student's ability to move beyond rigid VSEPR models and apply Molecular Orbital theory concepts (back-bonding) to both coordination complexes and main-group compounds.

The trap lies in assuming that isoelectronic complexes have identical bond lengths/frequencies, or that analogous molecules like $N(SiH_3)_3$ and $N(CH_3)_3$ share the same hybridization.

Students often overlook how synergic bonding dynamically alters bond order, bond length, and molecular geometry depending on the central atom's electronic environment.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Chemical Bonding and Molecular Structure - Class 11 Part 1
Concept	Bond Angle Variations
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free