Oxalates

The oxalate ion acts as a ligand and forms complexes, especially chelates, with many metal ions. The ion contains a planar octa-electronic π-system, which is particularly stable. It is a reductive anion. Rare earth oxalate is not very soluble in aqueous solution, and its solubility in hydrochloric acid, nitric acid, and sulfuric acid decreases as the acidity decreases. Oxalic acid is the precipitant of rare earth compounds, so oxalic acid rare earth as precipitation extraction of rare earth elements and preparation of rare earth oxides as the main method.