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JEE MainChemistryCoordination Compounds

Among the following octahedral complexes, which one has the highest spin-only magnetic moment?

Options

  1. A[CoF₆]³⁻
  2. B[RhF₆]³⁻
  3. C[IrF₆]³⁻
  4. D[Co(NH₃)₆]³⁺

Correct answer

A. [CoF₆]³⁻

Step-by-step solution

The spin-only magnetic moment depends on the number of unpaired electrons. All the given complexes contain the central metal ion in a +3 oxidation state and have a d^6 electronic configuration. For 3d series metals like Co³⁺ , fluoride ( F^- ) is a weak field ligand. Thus, ₀ For 4d and 5d series metals ( Rh³⁺ and Ir³⁺ ), the crystal field splitting energy ( ₀ ) is exceptionally large ( ₀ > P ) regardless of the ligand field strength. Therefore, [RhF₆]³⁻ and [IrF₆]³⁻ are low-spin complexes with 0 unpaired electrons

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