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Question #44869
The Question
The thiometallate anions \ce{[MoS4]^{2-}} and \ce{[WS4]^{2-}} both exhibit tetrahedral geometry. Due to the lanthanoid contraction, the ionic radii of \ce{Mo^{6+}} and \ce{W^{6+}} are nearly identical ( \AA). Based on the differences in their quantum mechanical electronic environments, identify the correct relationship between their tetrahedral crystal field splitting energies () and the energies of their lowest-energy Ligand-to-Metal Charge Transfer (LMCT) bands ().
Options
- A.
;
- B.
;
- C.
;
- D.
;
Check Your Answer
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
Post-Lanthanoid Radii Equality|Tetrahedral Splitting Patterns|EAN Rule (Sidgwick's Rule)
Why This Question Is Tricky
Common Mistakes
This question tests a classic 'Lethal Collision' in advanced inorganic chemistry: the conflation of steric size (ionic radii) with electronic orbital extension.
Students often erroneously assume that because the Lanthanoid Contraction makes the ionic radii of Mo and W nearly identical, their coordination complexes will have identical splitting energies () and electronic spectra (Option C).
However, the hidden variable is the radial extension of the 5d orbitals, which diverges from the ionic radius trend.
The 5d orbitals extend further, increasing ligand field splitting ().
Furthermore, the higher energy of the 5d orbitals in W(VI) compared to 4d in Mo(VI) increases the LMCT gap, testing the student's understanding of redox stability trends down a transition metal group.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | D and F Block Elements - Class 12 |
| Concept | Post-Lanthanoid Radii Equality |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |