Question
Given below are two statements:
Statement I: Both $\left\lbrack Co\left( {NH}_{3} \right)_{6} \right\rbrack^{3 +}$ and $\left\lbrack {CoF}_{6} \right\rbrack^{3 -}$ complexes are octahedral but differ in their magnetic behaviour.
Statement II: $\left\lbrack Co\left( {NH}_{3} \right)_{6} \right\rbrack^{3 +}$ is diamagnetic whereas $\left\lbrack {CoF}_{6} \right\rbrack^{3 -}$ is paramagnetic.
In the light of the above statements, choose the correct answer from the options given below:
Options
Solution
Sol. [Key Concept: Ligand field strength and magnetic behaviour]
Both complexes contain Co³⁺, a d⁶ ion, in an octahedral environment. In [Co(NH₃)₆]³⁺, the ligand field gives the low spin arrangement t₂g⁶e(g)⁰ with no unpaired electrons, so it is diamagnetic. [CoF₆]³⁻ is high spin t₂g⁴e(g)² with four unpaired electrons and is paramagnetic. Thus both statements are true, option (3).
Co³⁺ before ligand pairing 
With NH₃ 
With F⁻ 
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