Sodium ferrioxalate


Sodium ferrioxalate is a chemical compound with the formula. It is also called sodium oxalatoferrate or sodium trisoxalatoferrate.
The compound is a salt consisting of ferrioxalate anions,, and sodium cations. The anion is a transition metal complex consisting of an iron atom in the +3 oxidation state and three bidentate oxalate ions anions acting as ligands.
The ferrioxalate anion is sensitive to light and higher-energy electromagnetic radiation, which causes the decomposition of one oxalate to carbon dioxide and reduction of the iron atom to iron.

Properties

Solubility

This compound is very soluble in hot water,, but a lot less soluble in cold water,, about the solubility of sodium chloride. It is not appreciably soluble in ethanol or ethanol water mixtures which are more than 50% ethanol by mass. It is somewhat more soluble in water than the corresponding potassium salt.

Preparation

Sodium ferrioxalate can be obtained by mixing solutions of sodium oxalate and ferric oxalate, and waiting a few hours for the brown colour of the ferric oxalate to be replaced with the green colour of the complex anion.
The equilibrium is attained only slowly at room temperature. The product can then be crystallized by evaporating the solution at just below boiling until small crystals appear, then allowing it to cool. The product may also be precipitated by adding methanol or ethanol to the solution.
Some decomposition of the ferric oxalate may occur during the process, resulting in the canary-yellow insoluble iron oxalate. Small amounts of hydrogen peroxide may be added to keep the iron in the 3+ oxidation state.