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Question #44486

Difficulty: 8/10 | 🟢 Free

The Question

Consider the transition metal complexes $\ce{[Cr(H2O)6]^{2+}}$ (Complex I) and the pseudo-octahedral piano-stool complex $\ce{[W(\eta^5-C5H5)(NH3)3]^+}$ (Complex II). Both contain the metal center in a $d^4$ electronic configuration. Which of the following statements correctly describes the magnetic behavior and structural distortion of these complexes at $298\text{ K}$ ?

Options

A.
Complex I is paramagnetic with strong JT distortion; Complex II is diamagnetic with no JT distortion.
B.
Complex I is paramagnetic with strong JT distortion; Complex II is paramagnetic with weak JT distortion.
C.
Both complexes are paramagnetic and exhibit strong JT distortion.
D.
Complex I is diamagnetic with no JT distortion; Complex II is paramagnetic with strong JT distortion.

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

Aromaticity (Huckel’s Rule)|Crystal Field Splitting (Octahedral)|d-orbital contraction

Why This Question Is Tricky

Common Mistakes

The question tests the transition from standard octahedral Crystal Field Theory (CFT) to Molecular Orbital (MO) theory in organometallics.

The trap lies in treating the pseudo-octahedral $\ce{[W(\eta^5-Cp)(NH3)3]^+}$ complex as having a standard $t_{2g}^4$ low-spin configuration, which implies paramagnetism and weak Jahn-Teller distortion.

The 'hidden variable' is the $C_{3v}$ piano-stool splitting caused by the aromatic Cp ligand and the 5d lanthanide contraction, resulting in a completely filled $e^4$ diamagnetic ground state that overrides any JT distortion.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Hydrocarbons - Class 11 Part 2
Concept	Aromaticity (Huckel’s Rule)
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free