Oxalate (IUPAC: ethanedioate) is the dianion with the formula C2O42−, also written (COO)22−. Either name is often used for derivatives, such as salts of oxalic acid (for example disodium oxalate, (Na+)2C2O42−) or esters thereof (for example dimethyl oxalate, (CH3)2C2O4). Oxalate also forms coordination compounds where it is sometimes abbreviated as ox.
Many metal ions form insoluble precipitates with oxalate, a prominent example being calcium oxalate, the primary constituent of the most common kind of kidney stones.
Read more about Oxalate: Relationship To Oxalic Acid, Structure, Occurrence in Nature, As A Ligand, Safety