Oxalate (IUPAC: ethanedioate) is the dianion with the formula C 2O2− 4, also written (COO)2− 2. Either name is often used for derivatives, such as salts of oxalic acid, for example sodium oxalate Na2C2O4, or dimethyl oxalate ((CH3)2C2O4). Oxalate also forms coordination compounds where it is sometimes abbreviated as ox.