section_path: Compounds/Copper(III) and copper(IV)
section_name: Copper(III) and copper(IV)
paragraph_text: Copper(III) and copper(IV)
  
  Copper(III) is most often found in oxides. A simple example is potassium cuprate, KCuO, a blue-black solid. The most extensively studied copper(III) compounds are the cuprate superconductors. Yttrium barium copper oxide (YBa Cu O) consists of both Cu(II) and Cu(III) centres. Like oxide, fluoride is a highly basic anion and is known to stabilize metal ions in high oxidation states. Both copper(III) and even copper(IV) fluorides are known, K CuF and Cs CuF, respectively.
  
  Some copper proteins form oxo complexes, which, in extensively studied synthetic analog systems, feature copper(III). With tetrapeptides, purple-colored copper(III) complexes are stabilized by the deprotonated amide ligands.
  
  Complexes of copper(III) are also found as intermediates in reactions of organocopper compounds, for example in the Kharasch–Sosnovsky reaction.