Oxidation states of copper and sulfur
Bonding in copper sulfide cannot be properly described by simple oxidation state forms because the Cu-S bond is somewhat covalent rather than ionic and highly delocalized, resulting in a complex electronic band structure. Although many textbooks (eg ) give the mixed valence formula (Cu+)2(Cu2+)(S2−)(S2)2− for CuS, the X-ray photoelectron spectroscopy data strongly demonstrate that for simple oxidation According to the state formalism, all known copper sulfides should be considered as pure monovalent copper compounds, and the more appropriate chemical formulas are (Cu+)3(S2−)(S2)− for CuS and (Cu+)(S2) for CuS2, respectively −

Further evidence that the so-called "valence hole" should be assigned to the S2 units in these two formulas is the length of the S-S bond, which in CuS (0.207 nm) and CuS2 (0.203 nm) is significantly shorter than the "classical" disulfide Fe2+(S2)2− (0.218 nm). This bond length difference is attributed to the higher bond order in (S-S)− than in (S-S)2− because electrons are removed from the π* antibonding orbitals. [9] NMR studies of CuS have shown that there are two distinct species of copper atoms, one with more metallic properties than the other. [13] This apparent discrepancy with X-ray photoelectron spectroscopy data highlights the problem of NMR in determining the oxidation states of compounds of mixed valence. The issue of copper valence in sulfides (as well as selenides and tellurides) continues to be revisited in the literature. A good example is the 2009 study of the ternary compound CuCo2S4 [14], a spinel mineral called caroleite, "primarily with the aim of unambiguously determining the oxidation state of copper in the mineral" and obtaining Concluded "Experimental and simulated copper L2,3 absorption spectra identify a well-defined oxidation state of CuI in Carrollite bulk".
Copper sulfide is a family of compounds and minerals copper ii sulfide with the formula CuxSy. Both minerals and synthetic materials contain these compounds. Some copper sulfides are economically important ores.