Question

Write the formula of the following coordination compound.
Iron (III) hexacyanoferrate (II)

Answer 1

Hint: In the name iron (III) hexacyanoferrate (II), the numbers are in parenthesis in roman numerals indicating the oxidation state of iron atoms. The anion in the compound is hexacyanoferrate which has the formula$\,{[Fe\left( {CN} \right)6]^{ - 4}}\,$, also known as ferricyanide.

Complete step by step answer:
By definition, coordination compounds are molecules that possess one or multiple metal centers that's absolute to ligands (atoms, ions, or molecules that donate electrons to the metal). These complexes are neutral or charged. When the complex is charged, it's stabilized by neighboring counter-ions.
The formula of the complex anion hexacyanoferrate(II) is $\,{[Fe\left( {CN} \right)6]^{ - 4}}\,$ .
If the coordination complex carries a net charge, the complex is called a complexion. The compounds that contain a coordination complex are called coordination compounds.
Now, we know:
$ \Rightarrow $ The number of iron is $ + 2$ and every cyanide ion has $ - 1$ charge.
Hence, the net charge on the complex anion will be as follows:
$ \Rightarrow $\[\, + 2 + 6\left( { - 1} \right) = - 4\,\]
$ \Rightarrow $ $ - 4$ Net charge on the complex anion is going to be balanced by the $ + 3$ charge on $F{e^{3 + }}$ cations when the $\,3\;{[Fe\left( {CN} \right)6]^{4 - }}\,$ cations combine with the $\,3\;{[Fe\left( {CN} \right)6]^{4 - }}\,$ complex anions.
$\Rightarrow $ The formula of the compound Iron (III) hexacyanoferrate (II) is as following: $\,F{e_4}{([Fe{\left( {CN} \right)_6}])_3}\,$

So, the correct answer is Option A .

Note: A complexion encompasses a metal ion at its center with a sort of other molecules or ions surrounding it. These could also be considered to be attached to the central ion by coordinate (dative covalent) bonds and in some cases, the bonding is more complicated than that. The molecules or ions surrounding the central metal ion are called ligands.

Compared to normal cyanides like cyanide, the ferricyanides are much less toxic due to the tight hold of the $C{n^ - }$ to the $F{e^{3 + }}$. They react with mineral acids, although they release highly toxic compound gas.