Potassium ferrioxalate

Potassium ferrioxalate is a chemical compound with the formula K 3[Fe(C 2O 4) 3]. It often occurs as the trihydrate K 3[Fe(C 2O 4) 3]·3H2O. Both are crystalline compounds, lime green in colour. , also known as potassium trisoxalatoferrate or potassium tris(oxalato)ferrate(III).

The compound is a salt consisting of ferrioxalate anions, [Fe(C 2O 4) 3]3−, and potassium cations K+. The anion is a transition metal complex consisting of an iron atom in the +3 oxidation state and three bidentate oxalate ions C 2O2− 4 anions acting as ligands. Potassium acts as a counterion, balancing the −3 charge of the complex. In solution, the salt dissociates to give the ferrioxalate anion, [Fe(C 2O 4) 3]3−, which appears fluorescent green in color.

The ferrioxalate anion is quite stable in the dark, but is decomposed by light and higher-energy electromagnetic radiation. This feature is exploited for chemical actinometry, the measure of light flux, and for the preparation of blueprints.