question_answer

Which of the following complexes are inner-orbital complex and diamagnetic?

A)  \[{{[Fe{{(CN)}_{6}}]}^{4-}}\]    

B)  \[{{[Fe{{({{H}_{2}}O)}_{6}}]}^{2+}}\]

C)  \[{{[Cu{{(N{{H}_{3}})}_{6}}]}^{2+}}\]         

D)  \[{{[Ni{{(CN)}_{6}}]}^{4-}}\]

Correct Answer: A

Solution :

 In \[{{[Fe{{(CN)}_{6}}]}^{4-}},\,Fe\], is in +2 oxidation state. \[_{26}Fe-1{{s}^{2}},\,2{{s}^{2}}\,2{{p}^{6}},\,3{{s}^{2}}s{{p}^{6}},\,4{{s}^{2}}\] (\[C{{N}^{-}}\] is a strong field ligand and causes pairing of electrons.) Therefore,   \[{{[Fe{{(CN)}_{6}}]}^{4-}}\]   complex   ion   is inner-orbital and diamagnetic (as all electrons are paired).