Question

Arrange the following coordination compounds in the increasing order of magnetic moments. (Atomic numbers: Mn = 25, Fe = 26)

1. [FeF₆]³⁻
2. [Fe(CN)₆]³⁻
3. [MnCl₆]³⁻ (High spin)
4. [Mn(CN)₆]³⁻

Options

• A < B < D < C

• B < D < C < A

• A < C < D < B

• B < D < A < C

Answer 1

B < D < C < A

Explanation:

• [FeF₆]³⁻: Fe³⁺ (d⁵) with F⁻ (weak field) keeps Fe³⁺ high-spin, with 5 unpaired electrons and the highest magnetic moment.
• [Fe(CN)₆]³⁻: Fe³⁺ (d⁵) with CN⁻ (strong field) causes electron pairing, so there are 0 unpaired electrons and a low magnetic moment.
• [MnCl₆]³⁻ (High spin): Mn³⁺ (d⁴) with Cl⁻ (weak field) leads to high spin, 4 unpaired electrons and a higher magnetic moment.
• [Mn(CN)₆]³⁻: Mn³⁺ (d⁴) with CN⁻ (strong field) causes pairing, so there are 2 unpaired electrons and a moderate magnetic moment.

Correct order: [Fe(CN)₆]³⁻ < [Mn(CN)₆]³⁻ < [MnCl₆]³⁻ (High spin) < [FeF₆]³⁻