Question

The correct order of spin only magnetic moments for the following complex ions is

• A. [Fe(CN)₆]^3-< [CoF6]^3- < [MnBr₄]^2- < [Mn(CN)₆]^3-
• B. [Fe(CN)₆]^3-< [Mn(CN)₆]^3- < CoF₆]^3- < [MnBr₄]^2-
• C. [COF₆]^3- < [MnBr₄]^2- < [Fe(CN)₆]^3- < [Mn(CN)₆]^3-
• D. [MnBr₄]^2- < [CoF₆]^3- < [Fe(CN)₆]^3- < [Mn(CN)₆]^3-

Answer 1

The Correct Option is B

The question asks us to determine the correct order of spin-only magnetic moments for the given complex ions. To solve this, we need to calculate the number of unpaired electrons in each complex and use the formula for spin-only magnetic moment: \(\mu = \sqrt{n(n+2)}\ \text{BM}\), where n is the number of unpaired electrons. 

1. [Fe(CN)₆]^3-: Iron in this complex is in the +3 oxidation state. The electronic configuration of Fe³⁺ is 3d⁵. CN^- is a strong field ligand and causes pairing of electrons. Thus, the number of unpaired electrons = 1. Therefore, the spin-only magnetic moment is: \(\mu = \sqrt{1(1+2)} = \sqrt{3}\ \text{BM} \approx 1.73\ \text{BM}\).
2. [Mn(CN)₆]^3-: Manganese in this complex is in the +3 oxidation state. The electronic configuration of Mn³⁺ is 3d⁴. CN^- being a strong field ligand, leads to the pairing of electrons. The number of unpaired electrons = 2. Therefore, the spin-only magnetic moment: \(\mu = \sqrt{2(2+2)} = \sqrt{8}\ \text{BM} \approx 2.83\ \text{BM}\).
3. [CoF₆]^3-: Cobalt in this complex is in the +3 oxidation state. The electronic configuration of Co³⁺ is 3d⁶. F^- is a weak field ligand, so no pairing occurs. The number of unpaired electrons = 4. Therefore, the spin-only magnetic moment: \(\mu = \sqrt{4(4+2)} = \sqrt{24}\ \text{BM} \approx 4.90\ \text{BM}\).
4. [MnBr₄]^2-: Manganese in this complex is in the +2 oxidation state. The electronic configuration of Mn²⁺ is 3d⁵. Br^- is a weak field ligand, therefore no pairing occurs. The number of unpaired electrons = 5. Therefore, the spin-only magnetic moment: \(\mu = \sqrt{5(5+2)} = \sqrt{35}\ \text{BM} \approx 5.92\ \text{BM}\).

Based on the calculated magnetic moments, the order from least to greatest is: [Fe(CN)₆]^3- < [Mn(CN)₆]^3- < [CoF₆]^3- < [MnBr₄]^2-. Therefore, the correct answer is the second option:

[Fe(CN)₆]^3-< [Mn(CN)₆]^3- < [CoF₆]^3- < [MnBr₄]^2-

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