Discussion Forum



1)

 For the octahedral  complexes of Fe3+ in SCN- (thiocyanate- S) and in CN-  ligand environments, the difference between the spin only magnetic moments  in Bohr magnetons  (when approximated to the nearest  integer) is [ atomic number of Fe=26}


A) 3

B) 4

C) 1

D) 2

Answer:

Option B

Explanation:

 When S is donor atom of SCN- , it produces weak ligand field and forms high spin complex as 

 $\left[Fe \left(SCN\right)_{6}\right]^{3-};Fe^{3+}(3d^{5})=$

732021477_c6.JPG

Spin           only       magnetic        moment

    $(\mu_{s})=\sqrt{5(5+2)}BM=\sqrt{35}BM$

 In case of CN- ligand , carbon  is the donor atom, it produces strong field and forms low spin  complex as

                         $\left[Fe(CN)_{6}\right]^{3-}:Fe^{3+}(3d^{5})$

732021725_c7.JPG

 Spin only magnetic moment   $(\mu_{s})=\sqrt{1(1+2)}BM$

                           $=\sqrt{3}BM$

  Hence, difference  in spin  only magnetic moment

      $=\sqrt{35}-\sqrt{3}=4BM$