Alkali metal cuprates(III)
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In inorganic chemistry, alkali metal cuprates(III) refers to a family of copper salts of the form MCuO2, where M is an alkali metal. They are cuprate salts and coordination polymers. Their primary interest is as simple models of the polymeric cuprate(III) sheet anion, notionally CuO−2, which also appears in cuprate superconductors.
Potassium cuprate
One of the simplest oxide-based cuprates is potassium cuprate(III) KCuO2. This species can be viewed as the K+ salt of the polyanion [CuO−2]n. As such the material is classified as an oxide cuprate. This dark blue diamagnetic solid is produced by heating potassium peroxide and copper(II) oxide in an atmosphere of oxygen:[2]
- K2O2 + 2 CuO → 2 KCuO2
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.[3]
- 2 KO2 + 2 CuO → 2 KCuO2 + O2
It can also be synthesized by heating potassium superoxide and copper powder:[4]
- KO2 + Cu → KCuO2
KCuO2 reacts with the air fairly slowly. It starts to decompose at 760 K (487 °C; 908 °F) and its color changes from blue to pale green at 975 K (702 °C; 1,295 °F). Its melting point is 1,025 K (752 °C; 1,385 °F).[3][4]
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.[4]