Cuprate loosely refers to a material that can be viewed as containing anionic copper complexes. Examples include tetrachloridocuprate ([CuCl4]2−), the superconductor YBa2Cu3O7, and the organocuprates (e.g., dimethylcuprate [Cu(CH3)2]−). The term cuprates derives from the Latin word for copper, cuprum. The term is mainly used in three contexts: oxide materials, anionic coordination complexes, and anionic organocopper compounds. Oxides One of the simplest oxide-based cuprates is the copper(III) oxide KCuO2, also known as "potassium cuprate(III)". This species can be viewed as the K+ salt of the polyanion []n. As such the material is classified as a cuprate. This dark blue diamagnetic solid is produced by heating potassium peroxide and copper(II) oxide in an atmosphere of oxygen: K2O2 + 2 CuO → 2 KCuO2 Other cuprates(III) of alkali metals are known; in additional, structure of KCuO2, RbCuO2 and CsCuO2 has been determined as well. KCuO2 was discovered first in 1952 by V. K. Wahl and W. Klemm, they synthesized this compound by heating copper(II) oxide and potassium superoxide in an atmosphere of oxygen. 2KO2 + 2CuO → KCuO2 + O2 It can also be synthesized by heating potassium superoxide and copper powder: KO2 + Cu → KCuO2 KCuO2 reacts with the air fairly slowly. It starts to decompose at 760K and its color changes from blue to pale green at 975K. Its melting point is 1025K. RbCuO2 (blue-black) and CsCuO2 (black) can be prepared by reaction of rubidium oxide and caesium oxide with copper(II) oxide powders, at 675K and 655K in oxygen atmosphere, respectively. Either of them reacts with the air fast, unlike KCuO2. In fact, KCuO2 is a non-stoichiometric compound, so the more exact formula is KCuOx and x is very close to 2. This causes the formation of defects in the crystal structure, and this leads to the tendency of this compound to be reduced. Sodium cuprate(III) NaCuO2 can be produced by using hypochlorites or hypobromites to oxidize copper hydroxide under alkaline and low temperature conditions. 2NaOH + CuSO4 → Cu(OH)2 ↓ Cu(OH)2 + 2NaOH + NaClO → 2NaCuO2 + NaCl + Cuprates(III) are not stable in water, and they can oxidize water as well. 4 + 2 → 4CuO + ↑ + 4 Sodium cuprate(III) has reddish-brown color and turn black gradually because they decompose into copper(II) oxide. In order to prevent them from decomposing, they must be produced at low temperature and without light. Coordination complexes Copper forms many