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Which of the following complex ion is not expected to absorb visible light?

  • Option 1)

    \left [ Ni(CN)_{4} \right ]^{2-}

  • Option 2)

    \left [ Cr(NH_{3})_{6} \right ]^{3+}

  • Option 3)

    \left [ Fe(H_{2}O)_{6} \right ]^{2+}

  • Option 4)

    \left [ Ni(H_{2}O)_{6} \right ]^{2+}

 

Answers (1)

best_answer

As we learnt in 

Magnetic Moments (spin only) -

\sqrt{n\left ( n+2 \right )} where n= number of unpaired electron.

- wherein

Number of unpaired e^{-} s and corresponding magnetic moments

1\rightarrow 1.7\\2\rightarrow 2.8\\3\rightarrow 3.9\\4\rightarrow 4.9\\5\rightarrow 5.9

 

 To absorb visible light, the complex ion must leave a central atom with  impaired e^{-}s

Electronic  config of Ni^{2+}\::\:3d^{8}\:4s^{\circ}\:4p^{\circ}

In a complex with CN^{-},\:CN^{-} living the strong field ligand will pair up 3d electrons of Ni^{2+} and the complex will undergo d sp^{2} hybridization.

Electronic config of Ni^{2+} in [Ni(CN)_{4}]^{2-}

Because of an absence of unpaired e^{-}s [Ni(CN)_{4}]^{2-} will not absorb visible light.

 


Option 1)

\left [ Ni(CN)_{4} \right ]^{2-}

This option is correct.

Option 2)

\left [ Cr(NH_{3})_{6} \right ]^{3+}

This option is incorrect.

Option 3)

\left [ Fe(H_{2}O)_{6} \right ]^{2+}

This option is incorrect.

Option 4)

\left [ Ni(H_{2}O)_{6} \right ]^{2+}

This option is incorrect.

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Plabita

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