Question

IUPAC name of${K_3}\left[ {Fe{{\left( {{C_2}{O_4}} \right)}_3}} \right]$ is:
A. Potassium dioxalatoferrate (I)
B. Potassium dioxalatoferrate (III)
C. Potassium trioxalatoferrate (III)
D. Potassium triioxalatoferrate (II)

Answer 1

The Roman number present in the IUPAC name of the complex represents the oxidation state of the central atom. It should be kept in mind while naming a coordination compound that cation should be named before anion.

Complete step by step answer: The given compound is commonly known as potassium ferrioxalate is a chemical compound with a chemical formula of ${K_3}\left[ {Fe{{\left( {{C_2}{O_4}} \right)}_3}} \right]$. Before telling its name, let's calculate the oxidation state of $Fe$in this compound. Oxidation state refers to the valency of an element when present in the bonding with another element in a compound. We know that ${C_2}{O_4}$ is also known as oxalate ion with oxidation number -2. We also know that potassium has an oxidation state of $+ 1$. Since the 3 atoms of potassium are present so its combined oxidation state is +3. To overcome this positive oxidation state, is +3. The $\left[ {Fe{{\left( {{C_2}{O_4}} \right)}_3}} \right]$ should have an equal and opposite oxidation state because the compound on whole is electricity neutral. So, the oxidation of $\left[ {Fe{{\left( {{C_2}{O_4}} \right)}_3}} \right]$ should be$- 3$. Now let the oxidation state of Fe be ‘x’. we know that ${C_2}{O_4}$has an oxidation state of $- 2$. Since 3 molecules of ${C_2}{O_4}$are present, their combined oxidation state should be $3x( - 2) = - 6$. The sum of oxidation states of $Fe$and ${({C_2}{O_4})_3}$should be $- 3.$i.e.
$x + \left( { - 6} \right) = - 3$
$\Rightarrow$ $x = - 3 - \left( { - 6} \right)$
Or, $\left[ {x = + 3} \right]$
Hence, the oxidation number of $Fe$in the compound is$+ 3.$
So, the IUPAC name should be potassium Trioxalatoferrate (iii) because it cation potassium and 3 legends of oxalate ion present.
Hence the option (c) is the correct answer.

Note: ${C_2}{O_4}$is a bidentate ligand, i.e. it has two donor sites, and form 2 bond with a central metal atom, glycinate ion, acetylacetonate etc. are some more example or bidentate ligand.