Copper(I) sulfide 65678 218690368 2008-06-11T19:18:21Z Brichcja 1483333 /* Oxidation states of copper and sulfur */ Got rid of unsightly maths text '''Copper sulfides''' describe a family of [[chemical compound]]s and minerals with the formula Cu<sub>x</sub>S<sub>y</sub>. Both [[mineral]]s and synthetic materials comprise these compounds. Some copper sulfides are economically important [[ore]]s. Prominent copper sulfide minerals include Cu<sub>2</sub>S ([[chalcocite]]) and CuS ([[covellite]]). In the mining industry, the minerals [[bornite]] or [[chalcopyrite]], which consist of mixed copper-iron sulfides, are often referred to as "copper sulfides". In [[chemistry]], a "binary copper sulfide" is any binary [[chemical compound]] of the elements copper and [[sulfur]]. Whatever their source, copper sulfides vary widely in composition with 2 &le; Cu/S &le; 0.5, including numerous of [[non-stoichiometric compound]]s. ==Classes of copper sulfides== Copper sulfides can be classified into three groups: '''Monosulfides''', 1.6 &le; Cu/S &le; 2: their [[crystal structure]]s consist of isolated sulfide anions that are closely related to either [[close-packing|hcp]] or [[cubic crystal system|fcc]] lattices, without any direct S-S bonds. The copper ions are distributed in a complicated manner over interstitial sites with both trigonal as well as distorted tetrahedral coordination and are rather mobile. Therefore, this group of copper sulfides shows ionic conductivity at slightly elevated temperatures. In addition, the majority of its members are [[semiconductor]]s. '''Mixed monosulfide and disulfide''' compounds of copper contain both monosulfide (S<sup>2-</sup>) as well as [[disulfide]] (S<sub>2</sub>)<sup>n-</sup> anions. Their crystal structures usually consist of alternating hexagonal layers of monosulfide and disulfide anions with Cu cations in trigonal and tetrahedral interstices. CuS, for example, can be written as Cu<sub>3</sub>(S<sub>2</sub>)S. Several nonstoichiometric compounds with Cu:S ratios between 1.0 and 1.4 also contain both monosulfide as well as disulfide ions. Depending on their composition, these copper sulfides are either [[semiconductors]] or metallic conductors. At very high pressures, a '''copper disulfide''', CuS<sub>2</sub>, can be synthesized. Its crystal structure is analogous to that of [[pyrite]], with all sulfur atoms occurring as S-S units. Copper disulfide is a metallic conductor due to the incomplete occupancy of the sulfur p band. ==Oxidation states of copper and sulfur== The bonding in copper sulfides cannot be correctly described in terms of a simple oxidation state formalism because the Cu-S bonds are rather of [[covalent]] than [[Ionic_bond | ionic]] character and have a high degree of [[delocalization]], resulting in complicated [[electronic band structures]]. Although common textbooks often give a mixed valence formula (Cu<sup>+</sup>)<sub>2</sub>(Cu<sup>2+</sup>)(S<sup>2–</sup>)(S<sub>2</sub>)<sup>2–</sup> for CuS, spectroscopic data give strong evidence that, in terms of the simple oxidation state formalism, ''all'' the known copper sulfides should be considered as purely monovalent copper compounds, and more appropriate formulas would be (Cu<sup>+</sup>)<sub>3</sub>(S<sup>2–</sup>)(S<sub>2</sub>)<sup>–</sup> for CuS, and (Cu<sup>+</sup>)(S<sub>2</sub>) <sup–-</sup> for CuS<sub>2</sub>, respectively. The assignment of the valence hole to the S<sub>2</sub> units in these two formulas is evident because the S-S bonds are significantly shorter in CuS (0.207 nm) and CuS<sub>2</sub> (0.203 nm) than in the "classical" disulfide Fe<sup>2+</sup>(S<sub>2</sub>)<sup>2-</sup> (0.218 nm). This bond length difference is caused by the higher bond order in (S-S)<sup>-</sup> compared to (S-S)<sup>2-</sup> because the electrons are removed from an π* [[antibonding]] orbital. ==References== *Siew Wei Goh, Alan N. Buckley, Robert N. Lamb: ''Copper(II) sulfide?'', Min. Eng. '''19''', 204 (2006), [http://dx.doi.org/10.1016/j.mineng.2005.09.003 doi:10.1016/j.mineng.2005.09.003] *J.C.W. Folmer ''Holes in the valence band of copper chalcogenides'' Thesis 1981 Groningen State University (Neth). ==External links== *[http://www.mindat.org/min-27403.html Copper sulfides mineral information and data] [[Category:Sulfide minerals]] [[Category:Sulfides]] [[Category:Copper compounds]] {{inorganic-compound-stub}} [[ca:Sulfur de coure]] [[de:Kupfer(I)-sulfid]] [[ja:硫化銅]] [[nl:Kopersulfide]] [[pl:Siarczek miedzi(I)]]