Question

Arrange the following complex ions in increasing order of their crystal field splitting energy (\( \Delta_0 \)):
\(\text{[Co(NH}_3\text{)}_6]^{3+}, \, \text{[CoF}_6]^{3-}, \, \text{[Co(CN)}_6]^{3-}\)

Hint:

Ligand field strength influences the crystal field splitting energy (\( \Delta_0 \)). Cyanide (\( \text{CN}^- \)) is a strong field ligand, followed by ammonia (\( \text{NH}_3 \)), and fluoride (\( \text{F}^- \)) is a weak field ligand.

Answer 1

Crystal Field Splitting Energy (∆0) and Ligand Field Strength

The crystal field splitting energy (∆₀) depends on the ligand field strength. The order of field strength for ligands is:

CN⁻ > NH₃ > F⁻

Order of Increasing ∆₀:

[CoF₆]³⁻ < [Co(NH₃)₆]³⁺ < [Co(CN)₆]³⁻

Explanation:

• Cyanide (CN⁻) is a strong field ligand, causing a large splitting of the d-orbitals, leading to a high ∆₀.
• Ammonia (NH₃) is a moderate field ligand, causing moderate splitting.
• Fluoride (F⁻) is a weak field ligand, leading to the smallest splitting of d-orbitals.