Copper(II) oxalate is an inorganic compound with the chemical formula . The value of x lies between 0 (anhydrous form) and 0.44. One of these species is found as the secondary mineral moolooite (0.44 hydrate). The anhydrous compound has been characterized by X-ray crystallography. Many transition metal oxalate complexes are known.
Copper(II) oxalate, whether anhydrous or hydrated, is practically insoluble in all solvents, as it is a coordination polymer.
Copper(II) oxalate can be produced by precipitation from acidified aqueous copper(II) salts and oxalic acid or an alkali metal oxalate.
Upon heating to 130 ðC, the hydrated copper(II) oxalates convert to the anhydrous cupric oxalate. Further heating at higher temperatures under an atmosphere of hydrogen gives copper metal, suitable as a reagent.
The hydrates bind Lewis bases.
Hydrated copper(II) oxalate reacts with alkali metal oxalates and ammonium oxalate to give bis(oxalato)cuprate:
Copper oxalate is used as a catalyst for organic reactions, as a stabilizer for acetylated polyformaldehyde.