Copper monosulfide

Copper monosulfide
IUPAC name Copper sulfide
Other names Covellite Copper(II) sulfide Cupric sulfide
Identifiers
CAS number	1317-40-4 Y
PubChem	14831
ChemSpider	14145 Y
RTECS number	GL8912000
Jmol-3D images	Image 1
SMILES [Cu]=S
InChI InChI=1S/Cu.S Y Key: BWFPGXWASODCHM-UHFFFAOYSA-N Y InChI=1/Cu.S/rCuS/c1-2 Key: BWFPGXWASODCHM-BLKBWTQCAT
Properties
Molecular formula	CuS
Molar mass	95.611 g/mol
Density	4.6 g/cm3
Melting point	above 500°C (decomposes [2])
Solubility in water	insoluble
Solubility product, Ksp	1.27 x 10-36
Solubility	soluble in HNO3, NH4OH, KCN soluble in HCl, H2SO4
Refractive index (nD)	1.45 [1]
Related compounds
Other anions	Copper(II) oxide
Other cations	zinc sulfide
Y monosulfide (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Copper monosulfide is a chemical compound of copper and sulfur. It occurs in nature as the dark indigo blue mineral covellite. It is a moderate conductor of electricity. ^[3] A black colloidal precipitate of CuS is formed when hydrogen sulfide, H₂S, is bubbled through solutions of Cu(II) salts.^[4] It is one of a number of binary compounds of copper and sulfur (see copper sulfide for an overview of this subject), and has attracted interest because of its potential uses in catalysis^[5] and photovoltaics.^[6]

CuS structure and bonding

Copper monosulfide crystallizes in the hexagonal crystal system, and this is the form of the mineral covellite. There is also an amorphous high pressure form ^[7] which on the basis of the Raman spectrum has been described as having a distorted covellite structure. An amorphous room temperature semiconducting form produced by the reaction of a Cu(II) ethylenediamine complex with thiourea has been reported, which transforms to the crystalline covellite form at 30 °C.^[8]
The crystal structure of covellite has been reported several times,^[9][10][11] and whilst these studies are in general agreement on assigning the space group P6₃/mmc there are small discrepancies in bond lengths and angles between them. The structure was described as "extraordinary" by Wells^[12] and is quite different from copper(II) oxide, but similar to CuSe (klockmannite). The covellite unit cell contains 6 formula units (12 atoms)in which:

• 4 Cu atoms have tetrahedral coordination (see illustration).
• 2 Cu atoms have trigonal planar coordination (see illustration).
• 2 pairs of S atoms are only 207.1 pm apart ^[11] indicating the existence of an S-S bond (a disulfide unit).
• the 2 remaining S atoms form trigonal planar triangles around the copper atoms, and are surrounded by five Cu atoms in a pentagonal bipyramid (see illustration).
• The S atoms at each end of a disulfide unit are tetrahedrally coordinated to 3 tetrahedrally coordinated Cu atoms and the other S atom in the disulfide unit (see illustration).

The formulation of copper monosulfide as Cu^IIS (i.e. containing no sulfur-sulfur bond) is clearly incompatible with the crystal structure, and also at variance with the observed diamagnetism ^[13] as a Cu(II) compound would have a d⁹ configuration and be expected to be paramagnetic.^[4]
Studies using XPS^{[14][15][16][17]} indicate that all of the copper atoms have an oxidation state of +1. This contradicts a formulation based on the crystal structure and obeying the octet rule that is found in many textbooks (e.g. ^[4][18]) describing CuS as containing both Cu^I and Cu^II i.e. (Cu⁺)₂Cu²⁺(S₂)^2–S^2–. An alternative formulation as (Cu⁺)₃(S^2–)(S₂)^– was proposed and supported by calculations.^[19] The formulation should not be interpreted as containing radical anion, but rather that there is a delocalized valence "hole". ^[19][20] Electron paramagnetic resonance studies on the precipitation of Cu(II) salts indicates that the reduction of Cu(II) to Cu(I) occurs in solution. ^[21]

ball-and-stick model of part of the crystal structure of covellite	trigonal planar coordination of copper	tetrahedral coordination of copper	trigonal bipyramidal coordination of sulfur	tetrahedral coordination of sulfur-note disulfide unit

See also

• Copper sulfide for an overview of all copper sulfide phases
• copper(I) sulfide, Cu₂S
• Covellite

References

1. ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0070494398
2. ^ Blachnik, R.; Müller, A. (2000). "The formation of Cu₂S from the elements I. Copper used in form of powders". Thermochimica Acta 361 (1–2): 31–52. doi:10.1016/S0040-6031(00)00545-1 
3. ^ Wells A.F. (1962) Structural Inorganic Chemistry 3d edition Oxford University Press
4. ^ ^{a b c} Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. ISBN 0080379419. 
5. ^ Kuchmii, S.Y.; Korzhak A.V., Raevskaya A.E.,Kryukov A.I. (2001). "Catalysis of the Sodium Sulfide Reduction of Methylviologene by CuS Nanoparticles". Theoretical and Experimental Chemistry (New York: Springer) 37 (1): 36–41. doi:10.1023/A:1010465823376. 
6. ^ Mane, R.S.; Lokhande C.D. (June 2000). "Chemical deposition method for metal chalcogenide thin films". Materials Chemistry and Physics 65 (1): 1–31. doi:10.1016/S0254-0584(00)00217-0. 
7. ^ Peiris, M; Sweeney, J.S.; Campbell, A.J.; Heinz D. L. (1996). "Pressure-induced amorphization of covellite, CuS". J. Chem. Phys. 104 (1): 11–16. doi:10.1063/1.470870. 
8. ^ Grijalva, H.; Inoue, M.; Boggavarapu, S.; Calvert, P. (1996). "Amorphous and crystalline copper sulfides, CuS". J. Mater. Chem. 6 (7): 1157–1160. doi:10.1039/JM9960601157. 
9. ^ Oftedal, I. (1932). Z. Kristallogr. 83: 9–25. 
10. ^ Berry, L. G. (1954). "The crystal structure of covellite CuS and klockmannite CuSe". American Mineralogist 39: 504. 
11. ^ ^{a b} Evans, H.T. Jr.; Konnert J. (1976). "Crystal structure refinement of covellite". American Mineralogist 61: 996–1000. 
12. ^ Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications ISBN 0-19-855370-6
13. ^ Magnetic susceptibility of the elements and inorganic compounds
14. ^ Nakai, I.; Sugitani, Y.; Nagashima, K.; Niwa, Y. (1978). "X-ray photoelectron spectroscopic study of copper minerals". Journal of Inorganic and Nuclear Chemistry 40 (5): 789–791. doi:10.1016/0022-1902(78)80152-3. 
15. ^ Folmer, J.C.W.; Jellinek F. (1980). "The valence of copper in sulfides and selenides: An X-ray photoelectron spectroscopy study". Journal of the Less Common Metals 76 (1-2): 789–791. doi:10.1016/0022-5088(80)90019-3. 
16. ^ Folmer, J.C.W.; Jellinek F., Calis G.H.M (1988). "The electronic structure of pyrites, particularly CuS₂ and Fe_1−xCu_xSe₂: An XPS and Mössbauer study". Journal of Solid State Chemistry 72 (1): 137–144. doi:10.1016/0022-4596(88)90017-5. 
17. ^ Goh, S.W.; Buckley A.N., Lamb R.N. (February 2006). "Copper(II) sulfide?". Minerals Engineering 19 (2): 204–208. doi:10.1016/j.mineng.2005.09.003. 
18. ^ Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999), Advanced Inorganic Chemistry (6th ed.), New York: Wiley-Interscience, ISBN 0-471-19957-5 
19. ^ ^{a b} Liang, W.; Whangbo M, -H (February 1993). "Conductivity anisotropy and structural phase transition in Covellite CuS". Solid State Communications 85 (5): 405–408. doi:10.1016/0038-1098(93)90689-K. 
20. ^ Nozaki, H; Shibata, K; Ohhashi,N. (April 1991). "Metallic hole conduction in CuS". Journal of Solid State Chemistry 91 (2): 306–311. doi:10.1016/0022-4596(91)90085-V. 
21. ^ Luther, GW; Theberge SM, Rozan TF, Rickard D, Rowlands CC, Oldroyd A. (February 2002). "Aqueous copper sulfide clusters as intermediates during copper sulfide formation.". Environ. Sci. Technol. 36 (3): 394–402. doi:10.1021/es010906k. PMID 11871554.