Question

Which one of the following complexes is violet in colour ?

<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> JEE Main 2021

• A. $\left[Fe\right(CN{)}_{5}NOS{]}^{4-}$
• B. $\left[Fe\right(CN{)}_6{]}^{4-}$
• C. $F{e}_4\left[Fe\right(CN{)}_6{]}_3.H_{2}O$
• D. $\left[Fe\right(SCN{)}_6{]}^{4-}$

Answer 1

The correct option is A $\left[Fe\right(CN{)}_{5}NOS{]}^{4-}$

$\left[Fe\right(CN{)}_6{]}^{4-}$ - Plate yellow
$\left[Fe\right(CN{)}_6{]}^{3-}$ - Yellow
$Fe(SCN{)}_3$ - Red colouration
$\left[Fe\right(CN{)}_5\left(NOS\right){]}^{4-}$ - Violet colour

$N{a}_{2}S+\underset{\text{sodium nitroprusside}}{N{a}_2\left[Fe\right(CN{)}_{5}NO]}\to \underset{\text{sodium thionitroprusside (violet)}}{N{a}_4\left[Fe\right(CN{)}_{5}NOS]}$
​