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

\([CoF_6]^{3-:}\) \(Co^{3+} (d^6)\) with weak field ligand \(F^-\). Weak field ligands do not cause electron pairing, so: 

\(\uparrow \uparrow \uparrow \uparrow \uparrow \uparrow \quad (\text{u.e.} = 4)\)

\([MnBr_4]^{2-:}\) \(Mn^{2+} (d^5)\) with weak field ligand \(Br^-\). No pairing occurs 

:\(\uparrow \uparrow \uparrow \uparrow \uparrow \quad (\text{u.e.} = 5)\)

\([Fe(CN)_6]^{3-:}\) \(Fe^{3+} (d^5)\) with strong field ligand \(CN^-\). Strong field ligands cause electron pairing:

 \(\uparrow \downarrow \uparrow \downarrow \uparrow \quad (\text{u.e.} = 1)\)

\([Mn(CN)_6]^{3-:}\) \(Mn^{3+} (d^4)\) with strong field ligand \(CN^-\). Pairing occurs: \(\uparrow \downarrow \uparrow \downarrow \quad (\text{u.e.} = 2)\)

Order of magnetic moments: The spin-only magnetic moment is proportional to the number of unpaired electrons (u.e.): \([Fe(CN)_6]^{3-} < [Mn(CN)_6]^{3-} < [CoF_6]^{3-} < [MnBr_4]^{2-}\)