Copper oxidation state in chalcopyrite: Mixed Cu d9 and d10 characteristics

The determination of the oxidation states of copper and iron in sulfides, and chalcopyrite (CuFeS2) in particular, using 2p X-ray photoemission spectroscopy (XPS) and L2,3-edge X-ray absorption spectroscopy (XAS) is revisited. Reassessment of the published spectra derived by these methods produces consistent results and reveals the ‘d count’ in the copper compounds to be intermediate between d9 and d10. Nevertheless, these covalent copper compounds can be divided into those nominally monovalent and those nominally divalent. The Fe L2,3-edge XAS of chalcopyrite, along with Mössbauer data, confirm the presence of high-spin Fe3+. Chalcopyrite, despite recent published reports to the contrary, clearly belongs to the monovalent copper class.