Question

Correct order of spin only magnetic moment of the following complex ions is:
(Given At.no. Fe: 26, Co:27)

• A. $ [FeF_6]^{3−} >[Co(C_2O_4)_3]^{3−}>[CoF_6]^{3−}$
• B. $ [FeF_6]^{3−}>[CoF_6]^{3−}>[Co(C_2O_4)_3]^{3−} $
• C. $ [Co(C_2O_4)_3]^{3−}>[CoF_6]^3−>[FeF_6]^{3−} $
• D. $ [CoF_6]^{3−}>[FeF_6]^{3−}>[Co(C_2O_4)_3]^{3−} $

Answer 1

The Correct Option is B

The spin-only magnetic moment depends on the number of unpaired electrons.

 For [FeF$_6$]$^{3-}$, Fe$^{3+}$ has 5 unpaired electrons, resulting in the highest magnetic moment. 

For [CoF$_6$]$^{3-}$, Co$^{3+}$ in a weak field ligand (fluoride) has 4 unpaired electrons. 

For [Co(C$_2$O$_4$)$_3$]$^{3-}$, Co$^{3+}$ in a strong field ligand (oxalate) has 0 unpaired electrons. 

Thus, the order of magnetic moment is [FeF$_6$]$^{3-}$ $>$ [CoF$_6$]$^{3-}$ $>$ [Co(C$_2$O$_4$)$_3$]$^{3-}$.