Transition and InnerTransition Elements - Result Question 19
####20. Which of the following compounds is not yellow coloured?
(2015 Main)
(a) $Zn _2\left[Fe(CN) _6\right]$
(b) $K _3\left[Co\left(NO _2\right) _6\right]$
(c) $\left(NH _4\right) _3\left[As\left(Mo _3 O _{10}\right) _4\right]$
(d) $BaCrO _4$
Show Answer
Solution:
- $Zn _2\left[Fe(CN) _6\right], K _3\left[Co\left(NO _2\right) _6\right]$ and $\left(NH _4\right) _3$ As $\left[Mo _3 O _{10}\right] _4$ show colour due to $d$ - $d$ transition while $BaCrO _4$ is coloured due to charge transfer phenomenon.
Further according to spectrochemical series the strong ligand possessing complex has higher energy and hence lower wavelength. Therefore, complexes containing $NO _2, NH _4^{+}, O^{2-}$ etc., ligands show yellow colour while $CN^{-}$forces the complex to impart white colour.
Spectrochemical series
$I^{-}<Br^{-}<S^{2-}<SCN^{-}<Cl^{-}<NO _3^{-}<N _3^{-}<F^{-}<OH^{-}$
$<C _2 O _4^{2-} \approx H _2 O<NCS^{-}<CH _3 CN<$ py $<NH _3<$ en
$<$ bipy $<$ Phen $<NO _2^{-}<PPh _3<CN^{-} \approx CO$
