Copper(II) oxalate

Copper(II) oxalate are inorganic compounds with the chemical formula CuC2O4(H2O)_{x}. The value of x can be 0, 0.44, and 1. Two of these species are found as secondary minerals (degradation of minerals), whewellite (monohydrate and moolooite (0.44 hydrate). The anhydrous compound has been characterized by X-ray crystallography.  Many transition metal oxalate complexes are known.

Copper(II) monooxalates are practically insoluble in all solvents. They are coordination polymers.

Synthesis
Copper(II) oxalate can be produced by precipitation from acidified aqueous copper(II) salts and oxalic acid.
 * CuSO4 + H2C2O4 + H2O -> CuC2O4*H2O + H2SO4

Reactions
Upon heating to 130 °C, 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:
 * CuC2O4)(H2O)_{x} + C2O4(2-)  ->  [Cu(C2O4)2](2-)  +  x H2O

Uses
Copper oxalate is used as a catalyst for organic reactions, as a stabilizer for acetylated polyformaldehyde.

Related compounds

 * Cuprous oxalates.